Creatures:

Signal Pest

pros: 1 drop, bumps up your creatures when you attack, essentially a flyer, is an artifact

cons: does no damage by itself

Importance: 5/5 (main board)

Myr Sire

pros: 2 drop that replaces itself upon death, is an artifact

cons: none

Importance: 5/5 (main board)

Goblin Wardriver

pros: 2 drop, bumps up your creatures when you attack

cons: costs RR, not an artifact

Importance: 4/5 (side board for Myr Sire for games you need to fly in for more damage)

Sharding Sphinx

pros: can make a lot of thopters per turn late game possibly giving you a win, flying, is an artifact

cons: 6CC

Importance: 4/5 (main board)

Direct Damage

Galvanic Blast

pros: cheap, instant, creature or player

cons: full potential requires 3 artifacts but that shouldn't be too much of an issue

Importance: 5/5 (main board)

Shrapnel Blast

pros: instant, high damage, targets creature or player, cheap, can be used to kill off your Hangerback Walker when you want it to die

cons: have to sacrifice an artifact but the trade off is worth it

importance: 5/5 (main board)

Evasion

Sleep

pros: taps down all creatures for 2 turns allowing 2 all out attacks late game, can be used offensively or defensively, since it does not target it will still apply to Shroud/Hexproof creatures

cons: 2U cost, sorcery

importance: 5/5 (side board, use for decks with too many creatures or flyers)

Buffs

Weapon Surge

pros: cheap, affects all creatures, gives first strike, can be used for offense or defense, instant speed

cons: Wardriver may be a better option for offense, may not be all that important for your win condition

importance: 4/5 (main board)

Removal

Mana Leak

pros: It's Mana Leak, low cost low color weight counterspell

cons: It's Mana Leak, chance to be bypassed

importance 5/Mana Leak (mana board)

Vapor Snag

pros: cheap, instant, does 1 damage

cons: creature can return later, does 1 damage to yourself if you use it save your own creature, creatures only

importance: 4/5 (main board)

Disperse

pros: cheap, targets any permanent, use it to save anything of yours

cons: stuff can come back

importance: 5/5 (side board)

Rapid Hybridization/Pongify

pros: costs only U, instant, doesn't have a restriction like most removal, creature cannot regenerate, can kill big creatures your direct damages may not kill, can be used on your creatures in case you need a bigger blocker or access to a green creature, no one expects creature destruction from blue

cons: it gives the opponent a replacement creature

importance: 5/5 (side board)

NOTE: both cards do the same thing, Pongify is more $

Polymorphist's Jest

pros: mass effect, can be used offensively or defensively, instant speed, cheap CC, gets rid of abilities, shrinks creatures (possibly)

cons: UU in the cost, you have to find a way to kill off each creature

importance: 4/5 (side board)

Other

Impact Tremors

pros: extra damage for each creature that comes in, cheap cost, can be used in 2nd or 3rd games where you have to play defensively, could work nicely late game with Sharding Sphinx

cons: you may not have enough creature output for this strategy to work so it would help out in matches where you have to play defensively with well timed attacks to win

importance: 3/5 (side board); 4/5 with Sharding Sphinx in deck (side board)