Mono-Red Goblins. Santa is lord of the toy forge -- In the hall of the Snow-Covered Mountain King.
Playtest 1: Gauntlet of Might, Mana Echos, Thawing Glaciers, and Journeyer's Kite had a turn 8 win, with the following board:
Purphoros (pumped up 6 times), Kiki-Jiki, 2x Goblin Chieftain, 4x Goblin tokens, and Legion Loyalist swinging for 83 (40 unblockable)
Many choices are meta-driven. Comments, questions welcome.
My biggest issue with Goblin Assault is the forced combat phase. I have plenty of repeat offenders to generate tokens.
I'll try to avoid making this a giant ramble and just post a list of cards.
Firecat Blitz Add this card. Do it.
Goblin Offensive Same as above.
Blasphemous Act Excellent board wipe.
Gamble Basically the only red tutor.
Goblin Rally More tokens.
Insurrection Can win games all by itself. Pair it with a sac outlet and you're set to make everyone at the table cry.
Mogg Infestation You have 10 creatures on the board? No, now you have 20 and everyone at the table just took lethal from Purph. Amazing card, include it.
Molten Birth More tokens and sometimes repeatable.
Reforge the Soul Another wheel effect.
Skittering Invasion More tokens.
Into the Core Very good artifact removal.
Word of Seizing Stealing stuff is always fun.
Tooth and Claw Amaaaazing. Firecat Blitz or w/e for 10 tokens and turn them into another 5 for more delicious Purph dmg.
Thopter Squadron Combine with Mana Echoes and you get infinite mana and generates infinite dmg if Purph is out.
Solemn Simulacrum Ramp.
Grinning Ignus Basically reads 1R 2 dmg to each opponent. Also ramps up the storm count like crazy for Empty the Warrens.
Goblin Marshal Great value.
Emrakul's Hatcher Another token generator.
Beetleback Chief More tokens.
Genesis Chamber Crazy with Norin the Wary and lets you get more value out of your other creatures.
Myr Incubator Can instantly kill everyone at the table if you have enough artifacts in the deck. Not an auto include but could be fun to test.
Snake Basket Moooore tokens.
Zealous Conscripts Goes infinite with Kiki-Jiki.
Battle Hymn Enables some big plays with Firecat Blitz/Mogg Infestation etc.
Mana Geyser Better with more players. Meta dependent.
I feel like your list won't be fast enough. You might want some more manarocks.
Sol Ring Should be in just about every EDH deck.
Gauntlet of Power Can help your opponents but still really nice.
Unwinding Clock Untap those manarocks.
Voltaic Key More manarock untapping.
Oh you also might want to consider playing Goblin Ringleader . He goes really well with Goblin Recruiter , placing him ontop of all the goblins you grabbed with Recruiter and using him to draw them all at once the following turn.
Goblin War Strike with the goblin spam cards and low drops deadly.