I Really Want To Lose Friends (Modern)

Enchantments
Rancor: Cheap enchantment that returns itself if the creature it's attached to is killed or bounced back to your hand.

Instants
Giant Growth: Cheap buff spell.
Groundswell: Part of the turn 2 win combo; play a land on turn 2 with this in hand to add a +4/+4.
Massive Might: Cheap buff spell with trample.
Might of Old Krosa: Cheap buff spell that will almost always be cast on your main phase for a +4/+4 as part of the turn 2 win combo.
Mutagenic Growth: Free +2/+2 used for the turn 2 win combo.
Nature's Claim: Cheap artifact or enchantment destruction; we don't care about the opponent gaining life since we're winning through poison counters.
Unnatural Predation: Cheap buff spell with trample.

Sorceries
Explore: Cheap ramp and card draw.
Sylvan Scrying: Helps find lands but more importantly is useful for shuffling your deck on command.

Creatures
Blight Mamba: More of a later game infector that can be used if need be; mush better evasion thanks to it having regeneration.
Glistener Elf: Cheap infector and key for the turn 2 win combo; play the Elf turn 1 and buff it up later.

Sideboard
Naturalize: Cheap artifact or enchantment destruction with no lifegain for the opponent.
Plummet: Cheap flying creature destruction.
Reclaim: Cheap way to bring back creatures from the graveyard.
Snakeskin Veil: Cheap buff spell with hexproof to protect our creatures.
Sylvan Scrying: Helps find lands but more importantly is useful for shuffling your deck on command.
Tangletrap: Cheap flying creature and artifact destruction.
Titanic Growth: Cheap buff spell.
Wilt: Cheap artifact or enchantment destruction that can be cycled if it's a dead card in our hand.