Mono Red Sideboard/Last few slots.

Okay, so we have our main theme, and we have a fairly good fill-out of the last few slots.

To bring everyone up to speed:
Creatures: (13)
4x Stromkirk Noble
1x Grim Lavamancer
1x Spikeshot Elder
4x Stormblood Berserker
3x Phyrexian Metamorph

Non-Creature Permanents:  (10)
4x Shrine of Burning Rage
1x Ratchet Bomb
4x Koth of the Hammer
1x Batterskull

Spells: (12)
1x Faithless Looting3x Tezzeret's Gambit
4x Volt Charge 2x Devil's Play
2x Red Sun's Zenith

Lands: (24)

24x Mountain

+1 something.

So, I've been a horrifically bad side-boarder in the past, which is something we're looking to fix this time.  With Pyromancer Ascension the strategy was a bit easier, with Mono Red it seems like it matters alot more, so we need to think through each category of thing and see what we can do to improve our match-ups there.

Big (repeatable, game-ending) effects:

I really like the idea of having a sideboard card that doesn't necessarily answer a threat that the opponent's deck presents, but rather just murders their whole strategy.   Whether it be a recurring damage source, or a card that blanks their strategy, cards like this in sideboards can swing match-ups entirely, which is what we're looking for out of a sideboard card.  Sure, a card like Incinerate or Combust is a relatively efficient removal spell, but it's just a 1:1.  This category goes a lot bigger in general.

 I love me a red enchantment, and Mana Barbs is a potential game-ending threat against Ramp and Control.  If we had a Sulfuric Vortex, I'd be playing that, but Mana Barbs isn't too far off.  It's not a creature, it's hard to remove, it comes down relatively quick, and it just turns off a whole lot of cards.  You can't really Wolf Run, or Forbidden Alchemy, or even really Think Twice, Drownyard, or Snapcaster with this in play.  I need some testing against ramp, to see if this card lives up to my expectations in that matchup, but I am certain that this will be all I need against control.  (2-3 copies at most).  Control is already a pretty good mat-up, but if I can get double duty out of this guy against Ramp, it'll be a solid inclusion.  Against ramp, it needs to be accompanied by some sort of steal-effect, or a card like Inferno Titan, or Wurmcoil could just kill me.

Moltensteel Dragon seems like an awesome card against ramp.
1) It flies, which pretty much nothing they have does. (Inkmoth, sure, but we are red, right?)
2) It's a 4-drop, which is fast enough to matter.
3) It has four toughness, which avoids alot of their damage-based removal. (Slagstorm, Whipflare, Inferno Titan, non-metalcraft Galvanic Blast)
4) It potentially kills them on turn 5, which is just fast enough to matter, and combos pretty well with early aggression.  If they're even in the teens, this guy could get the job done in one swing.

4 (base) + 4 (normal firebreathing) + 1 (land drop) = attacking for 9 damage on turn 5, before I get around to spending any more life.  Now, realistically, I won't be higher than 16 when this guy comes out, and paying down to 2 is unlikely to be a strong plan unless they are tapped out.  This leaves 12 more life to spend, which is 15 "safe" damage just from this guy on turn 5.  This guy feels super-solid against ramp.

Some of the other cards in other sections hard-answer other strategies.  Ratchet bomb is a one-sided wrath against tokens, a deck that can block you all day long.  Inferno Titan ends games against aggro.  But we'll talk about those in a minute...

1 damage effects:

The first category of thing that red side-boarding offers is small (one damage) effects.  They are quite plentiful, and they have some good options with the rest of the deck.

The things we'll be looking to kill with this sort of effect are often (always) on turn one, and include the following cards:

The enemy:

These cards are the pinnacles of one-drops, and the ones we need to be reacting to turn one, or they quickly get out of control.  All of these quickly turn into (or enable) some very dangerous starts for your opponent .  We can't just drop our own Noble, and ignore this sort of effect from our opponent, like we might with, say other one-drops like Doomed Traveler, a spirit token on Turn 3, or a random dork like Young Wolf.

Your effect has to happen on your turn one (on the draw), or perhaps your turn two (on the play).  On the play, we get some help from our 4 x-spells that are not coming out in these match-ups.  This strongly influences what type of card we can use to deal with these cards.

Cards like Grim Lavamancer, or Spikeshot Elder, for example, are not going to cut it to deal with these cards in the early game.  The same goes for Inferno Titan, or Chandra, which naturally prey upon these type of cards in a vacuum.

General contenders for the "do one damage" category that handle these cards (aka on turn one)

The answers:

I think it is quite interesting to look at these cards for the purpose of dealing with opposing one-drops, since they directly compete for slots dealing with this specific problem.  They don't come in in match-ups where these problem cards above are not present.

Goblin Arsonist is the "best" one-drop for enabling a powered-up T2 Berserker.
Gut Shot can deal with the problem, while still allowing you to drop a Noble.

However, I think the best of these options is actually Forge Devil(!).
Forge Devil kills all of these creatures, and leaves behind the same 1/1 as Noble, that enables your Berserker quite nicely, without even needing to draw the Noble.  It seems like a perfect mix of all three cards.  It kills the threat, it stays around as a threat to power up Berserker, or eat removal, or apply pressure.  The damage is front-loaded, so it is not hurt as much by Vapor Snag, etc etc.

It isn't an amazing main-deck option, because it can't be cast T1 on the play, but you wouldn't play Gut Shot T1 on the play, you'd just play the Noble you always have in your hand.  Forge Devil even does less damage to you than Gut Shot, in the scenario where it matters...  It chumps to save Koth, it does almost everything in the scenario where it's good.  And in the scenario where it's bad?  Well, it's a sideboard card, you don't bring it in against Ramp or Control...

It's worst against killing things in response to equips, but equipment is seeing a downswing due to the amount of removal people are playing, and we're Red FFS, if we can't deal with an artifact, noone can....

The other one-damage answers:

These two are fine main-deck answers, and repeatable "free"-ish damage is pretty good against creature decks.   However, we can't overdo it with either of these as answers, because we don't have a ton of free "fuel" for Lavamancer, and Elder is quite spendy.  Both are somewhat lacking in multiples, so I'd set the limit on each of these as 1x Main, 1x Side. (4x total)

These last two consist of a kill condition in one card, and a card that sort of works with the deck's theme, and is often dead even in it's good matchup.

Inferno Titan is a serious house.  He represents 18 damage on an open board the turn after you cast him, and he clears up a battlefield quite well.  He's pretty reasonable against Vapor Snag (as all Titans), but he would be the most expensive spell in the deck.  24 lands is quite a bit for an aggro deck, and I do have 4 card draw spells, but I could still have a hard time getting him down, especially since one of my card draw spells encourages me to dump lands.  I like this guy in all the situations where Berserker and Noble are perhaps not the best.

Chandra, oh Chandra.  I really want this version of Chandra to be good, but she is just so... slow, and ineffective.  I'd play Liliana in a Heartbeat if she was red, because she solves a lot of problems the deck has.  But Chandra is a 4-mana Gut shot, with the benefit of being able to cast a Gut Shot every turn!  Her ultimate is similarly lackluster, and 1 damage effects are very hard to be relevant in that stage of the game.  White decks have Anthem effects by this time, Green have their big guys down, Blue's are 2/2s, Black's are x/2's, and Red guys are barreling down on you, killing her through the air.  I wish there was a good match-up for her, or that her effect was strong.  Without anthems, I think she might see play, but...

Among these options, I'd want at MOST
1x Inferno Titan (side)
1x Grim Lavamancer Main/1x Side
1x Spikeshot Elder Main/1x Side
1-3x Forge Devil (Side)

Sweepers:

White and Black get a lot of credit for having sweepers, but Red is the color people turn too quite often for sweep effects.  For our deck, this is somewhat of a double-edged sword.  We have a fair number of low-drops we'd want to cast early, and following that up with a sweeping creature-kill spell seems like not the best plan in the world.

However, if you look at our plan vs the creature match-ups, some of our creatures are not that amazing there.  Noble is terrible against non-human blockers, and Berserker isn't great if they have one-drops (because you can't get in for damage to pump him up).   Elder and Lavamancer aren't exactly strong turn one plays, and we're the one with the sweeper, so we can know whether we need to play slow or fast.  So let's look at what we have available, and see what kind of trouble we can get ourselves into...

Ratchet Bomb is an amazing card in this format.  It is very good against Tokens (while ignoring virtually everything in our deck), it is reasonable against white removal (which tends to be 3cc Exile perminants), and okay against Anthems (which are all 2cc).  We could play as many as three of this spell, and not look too silly, in the right match-up.

Contagion Engine is something that works pretty well with the deck (one-turn ultimate koth on 8 mana), but alot of our proliferate effects would in theory be coming out when these come in.

Whipflare and Slagstorm are both interesting.  Slagstorm seems like it "does the job" a bit better, because it deals with multiple anthems against tokens, single anthems against humans, double lords in UW/UB, and can go to the head in a pinch.  Whipflare is something our creatures are more likely to live through, and does kill unaugmented creatures quite well (Geist, Captain, etc)

Blasphemous Act is the best spell to T4 Koth into.  It potentially costs 1 if we're in the right situation (8 creature on board, including ours), and it sets up a clear ultimate the next turn.  This would be the spell I'd want to bring in if I was keeping the majority of my low-drops in.  It near-guarantees ultimate the next turn, which an aggro deck is unlikely to beat.

I'm really not sure which way to lean in this category.  There are just too many upsides to each option here for me to make a clear decision.  It's also possible that any of the pure sweepers (the red cards) are "too cute" for this application.

Artifact == Boom!

Manic Vandal is the standard, but I'm pretty sure Torch Fiend is just better.  It is the only instant speed one, and it beats down while you wait for them to have an artifact worth killing.  It can be killed before they play their artifact but you can always hold it if you suspect this, so it seems like it is just better than Manic Vandal, unless it's very likely that they will have an artifact to destroy by the time you're ready to cast your spell.  So, there you go.

Lifegain

I don't have a ton of creatures, so though sword might be the worst option here, strangely.  It is the fastest possible option, potentially being active on turn four.  It also gives some relevant protections (from my own sweepers?), and blocking avoidance.  Other swords might compete on this removal-protection and blocker avoidance, but sword certainly hits the hardest of the sword options.  However, I'm also more of a grindy deck, than a super-aggressive one....

Wurmcoil is one of the better options that exists, and it and Batterskull fight it out for which is the worst against Vapor Snag.  When in doubt, I'd say go with the cheaper one, and that is Batterskull.  Besides, equip my one-of Elder with my one-of Batterskull?  Good game?

I'd say either Batterskull or Wurmcoil are the competition for this slot, as a 1-3 of total between main and side.  They are also competing with some of the sweepers (Contagion Engine), or other random expensive cards (Inferno Titan).  It's possible that Titan is just the best "Life Gain" option, because it kills them in 1 turn, and does something immediately when it comes into play.  All three of these are excellent to copy with a Metamorph, and stand on their own, which is critical for this type of card.  A sword is great, but "what is it, compared to the arm that wields it".  If they wrath you, and you have a sword, your Metamorph is looking pretty sad.

Graveyard Hate:

For this category, we have an atomic bomb, and a tactical nuke:

 I think Surgical wins this fight for our deck, because against the decks where this matters (Reanimator), being able to "Time walk" their Unburial Rites, and get one more swing in is what we'd be looking to do.  These decks don't have sweepers, so we'd be keeping with the creature plan, and just buying a turn free of Elesh/Wurmcoil to seal the victory.  I don't think it would be reasonable to go over ~3 of this type of effect, and you'd have to believe that the deck was quite popular to go that high.  It does work fairly well against some of the undying creatures as well, so you might get some double-duty there.

If I had more artifacts, (to enable Mox Opal), I'd love to have some spellbombs, but we just can't get there without giving up a bit much.

Theft:

Instant speed, vs Trample.  Ray of Command is a serious beating, but Traitorous blood actually costs 3, which can set up some insane T6 plays with Metamorph.  (Take your Titan, Shoot itself, deal 9, copy your Titan, kill your titan).  Traitorous blooding a deathtouch creature (like Titan) is a big game as well.  But instant-speeding it against Elesh Norn turns their one-sided Wrath into a more palatable

This sort of effect could compliment a card like Mana Barbs to "finish them" with their own spells.

Random:

 Refugee is one of the best cards you can have for the red mirror, but it did not work out at all against match-ups with "red removal", like ramp.  Since MR is claimed to be dead in tournaments these days, this guy is probably taking a back seat to cards for other match-ups.

I played against quite a bit of blue control, and those guys really liked to bring Negate in against me, or leave in other counterspells.  Waif is probably the best guy to punish such a strategy.  However, he fights into the commonly paired black color, who has cheap creature removal, and sweepers, neither of which this guy is very good against.  He's also pretty abysmal against "deck with a one-drop", which comprises something like 60+% of the metagame right now.  If you add in one-drop removal, it's more like 100%.  Mons Goblin Raiders is not what we want.

Besides, we have some other cards that murder UB control, and avoid the creature problem.  Mua ha ha...

Mid-Stage Summary:

The best cards, with the maxes I'd want are:
3x Mana Barbs
3x Moltensteel Dragon
3x Traitorous Blood
3x Forge Devil
2x Gut Shot
1x Spikeshot Elder (+1x Main)
1x Grim Lavamancer (+1x Main)
2x Inferno Titan
2x Ratchet Bomb (+1x Main)
2x Slagstorm/2x Blasphemous Act
3x (Manic Vandal/Torch Fiend)
1x Wurmcoil Engine (+1x Batterskull Main)
2x Surgical Extraction

So, that's 26\8 cards.
If we group these by matchup:
Ramp:
3x Mana Barbs (?)
3x Moltensteel Dragon
3x Traitorous Blood
Against Ramp, I can take out the Shrines (4), Lavamancer/Elder (2), Fireballs (4).  So 10 is the max I'd want here.  If I could "double up" on the mana barbs here, and not need the traitorous blood because of Moltensteel, I could leave in some of these cards, because they are not horrific.  If I bring in the Mana Barbs, would I rather have Traitorous Blood, or Moltensteel?  If I bring in Mana Barbs, is Shrine, a normally bad card, suddenly a good card?  so -4 Fireball, +3 Shrine, +2 Moltensteel -1 Elder?

I need some test-time against ramp with this strategy, and we'll see how it works...  Maybe just Mana Barbs is enough, and I go up to a full 4 against Control and Ramp, enough said...

Control:
3x Mana Barbs
(Ratchet Bomb against O-Ring)
Against Control, I can take out the Fireballs (4), or the Elder/Lavamancer (2) + Berserker (4).  It really depends on how they want to play against me.  Elder/Lava are pretty terrible against Curse of DH, which most people will bring in or keep in, and Berserkers are rarely powered in this match-up (but if they are, they're game-ending).  I need must-answer threats though, to make them tap out, so I can resolve my game-ending threats (Shrine, Koth, Barbs, etc, etc)

Aggro:
3x Forge Devil
1x Spikeshot
1x Lavamancer
2x Inferno Titan
2x Ratchet Bomb
1x Wurmcoil
2x Slagstorm/2x Blasphemous Act.
I have trouble against (white) aggro, because my creatures don't connect, which causes a chain reaction of suck.  Flyers also get through against my Koth, making it a worse win condition.

Noble's okay in this matchup, because he's still hard to block, but Berserker gets alot worse.

The big question is what do I take out?  Do I fight the creature battle, trying to come out on top, or do I play sweepers, and if so, which ones?  Is Ratchet Bomb my sweeper, against their 3's of O Ring and Fiend Hunter?  (and Crusader, but that shouldn't be in?)  Do I bring in the life gain aggro trumps?  They combo well with the sweepers...

So really this is:
3x Forge Devil
1x Spikeshot
1x Lavamancer
1x Inferno Titan
(Taking out card draw?  Shrine?)

OR
2-4x Sweeper
2x Inferno Titan
1x Wurmcoil
0-1x Mimic Vat
(Taking out Berserker)

Tokens:
2x Ratchet Bomb
2x Inferno Titan
2x Slagstorm/2x Blasphemous Act
1x Wurmcoil

Random:
2x Surgical

Ratchet bomb, and splash hate for whichever plan I choose above, should be good.

Conclusion

3x Mana Bars (4x if good against Ramp)
2-3x Moltensteel or Traitorous blood, depending on testing results against ramp
2x Ratchet Bomb
1x Inferno Titan
5x other sideboard cards against Aggro (depending on plan/test results)
2-3x Random (Surgical, Mimic Vat, etc)