Fleshgrafter

Discard an artifact card: Fleshgrafter gets +2/+2 until end of turn.

Skywing Aven

Flying
Discard a card: Return Skywing Aven to its owner's hand.

Olivia's Dragoon

Discard a card: Olivia's Dragoon gains flying until end of turn.

Barbarian Bully

Discard a card at random: Barbarian Bully gets +2/+2 until end of turn unless a player has Barbarian Bully deal 4 damage to them. Activate only once each turn.

Trespasser il-Vec

Discard a card: Trespasser il-Vec gains shadow until end of turn. (It can block or be blocked by only creatures with shadow.)

Neurok Prodigy

Flying
Discard an artifact card: Return Neurok Prodigy to its owner's hand.

Dwarven Strike Force

Discard a card at random: Dwarven Strike Force gains first strike and haste until end of turn.

Hell-Bent Raider

First strike, haste
Discard a card at random: Hell-Bent Raider gains protection from white until end of turn.

Pulsating Illusion

Flying
Discard a card: Pulsating Illusion gets +4/+4 until end of turn. Activate only once each turn.

Skyshroud Vampire

Flying
Discard a creature card: Skyshroud Vampire gets +2/+2 until end of turn.

Ephemeron

Flying
Discard a card: Return Ephemeron to its owner's hand.

Cephalid Inkshrouder

Discard a card: Cephalid Inkshrouder gains shroud until end of turn and can't be blocked this turn. (A creature with shroud can't be the target of spells or abilities.)

Putrid Imp

Discard a card: Putrid Imp gains flying until end of turn.
Threshold — As long as seven or more cards are in your graveyard, Putrid Imp gets +1/+1 and can't block.

Psychatog

Discard a card: Psychatog gets +1/+1 until end of turn.
Exile two cards from your graveyard: Psychatog gets +1/+1 until end of turn.

Thalakos Drifters

Discard a card: Thalakos Drifters gains shadow until end of turn. (It can block or be blocked by only creatures with shadow.)

Thalakos Scout

Shadow (This creature can block or be blocked by only creatures with shadow.)
Discard a card: Return Thalakos Scout to its owner's hand.

Kozilek, the Great Distortion

When you cast this spell, if you have fewer than seven cards in hand, draw cards equal to the difference.
Menace
Discard a card with mana value X: Counter target spell with mana value X.

Pardic Lancer

Discard a card at random: Pardic Lancer gets +1/+0 and gains first strike until end of turn.

Ravenous Bloodseeker

Discard a card: Ravenous Bloodseeker gets +2/-2 until end of turn.

Vampire Hounds

Discard a creature card: Vampire Hounds gets +2/+2 until end of turn.