Left to decide: 4x1-of

I really like the 4x 1-of principle.  Normal PA theory says play 4-ofs, and lands.  However, this version of the PA deck has so many ways to "free" charge the PA, that we can have a few splash cards to fill in holes the deck has, and provide some strong utility.  In the past, we had to get our utility from 4-ofs, so we basically had to use Into the Roil, because it was the best general solution we could play as a 4-of.

However, now with easy charging, we can just throw in some 1-ofs to round out the last slot, and we can have our utility, and also have our PA's.  We see so many cards during a normal game, that we can expect to draw a 1-2-of at a reasonable frequency, perhaps every other game, presuming we want to draw it.

The cards need to solve problems the deck has.  The deck has a relatively hard time:
1) Dealing with super-swarm creature decks.  (Because Pyroclasm is bad as a 4-of)
2) Dealing with recursive creatures.  (Because you have to keep killing them)
3) Having some "action" after you've found and charged your ascension.  (So you don't run out of cards, and die anyway)

The poster-card for this is Foresee.

Foresee is pretty much the best spell you can cast to find Pyromancer Ascension.  It is twice as good as Preordain or Jace's Ingenuity, and three times as good as pretty much any other spell.  Being able to ship 4 cards, or draw the best card in the top 4 and a random card is simply amazing.

Foresee is also pretty much the best spell you can cast once you are Ascended.  There's no card I'd want to draw off the top with 8 mana, than this.  It draws more physical cards and looks at more cards, than pretty much any other spell.

Preordain is awesome, but only because it costs U instead of U3, and both find you action to keep going.  Every Foresee that I put in is two more Preordains, which is pretty hard to resist.

I wouldn't play more than two of these, because it does cost 4 mana, but playing one seems clearly better than playing 0.

Putting some spells like this into the deck can dramatically change what your deck is capable of, while still staying "on track" for the general theme of the deck.

What are some other options for this type of slot?

Shatter is pretty good in this metagame.  Sword of War and Peace, Batterskull, Spellskite, and Argentum Armor are nigh-impossible to beat without a card like this in the deck.  Into the Roil can do some of this as a delay option, but it's alot better to just kill it, than to bounce it.

Pyroclasm as a one-of main-deck could really mess some people up.  It's "better" than Arc Trail for clearing out swarms, and will rarely be dead.  (Exarch-Twin, ug)  It is cheap, and powerful, which are things we're looking for out of this sort of slot.  If we put a Pyro in, we can probably afford to play something like See Beyond instead of Arc Trail for the 4-of slot.

Surgical Extraction seems like an awesome card to have at least in the sideboard as a 1-of.  It answers some seriously problematic creatures, like Vengevine and Bloodghast for a very low cost.  It also does a number on ExarchTwin, presuming you deal with one copy of one of their spells (not guaranteed).  It is a reasonable answer to Squadron Hawk (easy to kill the first one), or as an answer to their answer to Pyromancer Ascension, once they play it.  Being able to see their plan, and their hand, puts this into a kind of super-Gitaxian-Probe like slot, where you have a shot at destroying part of their plan, instead of drawing a card.  Extracting a super-card like Jace,  Primeval, or Valakut could also do a number on the plan of some decks.  Even just Extracting Preordain could have some value.  Not a incredible card, but one to keep in mind, that won't show up on most of my filters for PA cards.

Call to mind is one card in this list thas is better as a two-of than a one-of.  Being able to CTM your CTM + one other card is a good way to grind out some longer games, and reuse some of these other one-ofs.  Surreal Memoir is "better" at getting more cards earlier, but Call to Mind replaces the word "random" with the word "Target", and shaves off a point of mana.  It can also get key Sorceries (like Foresee, Preordain, Pyroclasm) that Surreal Memoir can't.  Surreal is probably better if there is only one slot for this, Call to Mind is better for two.

Let the crazyness begin!  Before you dismiss this entirely, there are a few things to consider about this spell.   It is an easier-to-cast Searing Blaze, that does twice as much damage to the player.  It's a colorless token, so it blocks sworded creatures.  It sticks around to attack them.  It gets value out of leaving mana up (it's an instant).  It is an absurd 12 damage once Ascended that is immune to sorcery speed removal (assuming you ambush them at their end of turn).   It is big enough to kill Titans, and it kills Kor Firewalkers.  (Even with swords!)  It blocks (sworded) Gideons without dying.  It kills planeswalkers fairly well, because it tramples.  It doesn't deal with flying creatures (Squadron Hawk, Vampire Nighthawk, Consecrated Sphynx) that well, but that's really the only chink in it's armor.  It is an anti-creature card, that is never truly dead.  Casting it for the full 6 against a "control" deck isn't awesome, and it does turn on creature/artifact removal, so it is not entirely upside, but it could be incredible in the main, or the board.

An alternative to Surgical Extraction, this card doubles as a kill condition, as well as removal for pesky Vengevines and Bloodghasts.  It's far more expensive than Surgical Extraction, but it may fit the theme of the deck better, and be less dead in the other matchups.

Deprive is one of the better counterspells because it is a hard counter, that allows you to re-use Halimar Depths.  Its cost is fairly steep (UU) in our mostly R deck, but having a singleton counterspell of some type (Mana Leak, Negate, Spell Pierce) could be solid

Other considerations:

Phyrexian Mana:

Noxious Revival (put a card from your graveyard on top of your library.  can regrow your PA's)

Dismember (-5/-5 for 1PBPB, aka 1 + 4 life)

Sorceries:

Demolish (destroy land/artifact for 3R)

Devistating Summons (sac lands for cretaures - sideboard only obviously - terrible against Jace/Gideon)

Recurring Inisght (6 mana draw-spell with rebound)

Rite of Replication (clone, with multikicker)

Slagstorm (3 damage to players, or creatures for 1RR)

Surreal Memoir (random instant regrowth, with rebound, 3R)

Instants:

Act of Aggression (type)

Aether Tradewinds (bounce one of yours and mine for 2U)

Blue Sun's Zenith (UUU)

Combust (Sideboard)

Comet Storm (multikicker fireball)

Fuel for the Cause (Counter->Proliferate for UU2)

Into the Core (2RR, exile two target artifacts, instant)

Into the Roil (bounce/draw for 1U, 2UU)

Permafrost Trap (multi-tap trap)

Redirect (you choose targets for a spell, UU)

Reverberate (Fork, RR Instant)

Ricochet Trap (R counterspell/redirect)

Spell Contortion (counter/draw)

Turn Aside (U, counter a spell that targets PA, doesn't work on creatures)

Twisted Image (swap Power/toughness, draw a card for U, instant)

Twitch (twiddle, draw a card for 2U)

Unstable Footing (Damage can't be prevented, kicker do 5 damage for R, RR3)

Whiplash Trap (multi-unsummon trap)

Conclusions:

If my 4x is a burn spell (Searing Blaze/Arc Trail/Burst Lightning),

1x Foresee (Great at finding PA, great at getting action post-PA)

1x Shatter (RW Sword, Batterskull, Argentum Armor, Spellskite)

If my 4x is a draw spell (See Beyond, Gitaxian Probe)
1x Shatter
1x Pyroclasm
1x Red Sun's Zenith

I wouldn't mind having some recursion, either 2x Call to Mind, or 1x Surreal Memoir.

It is pretty frustrating the number of combinations I have to go through.  Just being able to make the call between the two draw spells and the three burn spells as the 4x would make picking the 1xes alot easier.