Skyshroud Vampire

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

Barbarian Bully

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

Neurok Prodigy

Flying
Discard an artifact card: Return this creature to its owner's hand.

Olivia's Dragoon

Discard a card: This creature gains flying until end of turn.

Ravenous Bloodseeker

Discard a card: This creature gets +2/-2 until end of turn.

Thalakos Scout

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

Thalakos Drifters

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

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.

Vampire Hounds

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

Skywing Aven

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

Ephemeron

Fleshgrafter

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

Cephalid Inkshrouder

Discard a card: This creature 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.)

Psychatog

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

Pardic Lancer

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

Putrid Imp

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

Trespasser il-Vec

Hell-Bent Raider

First strike, haste
Discard a card at random: This creature gains protection from white until end of turn.

Dwarven Strike Force

Discard a card at random: This creature gains first strike and haste until end of turn.

Pulsating Illusion

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