Marauding Mako

Whenever you discard one or more cards, put that many +1/+1 counters on this creature.
Cycling {2} ({2}, Discard this card: Draw a card.)

Scrounging Skyray

Flying
Whenever you discard one or more cards, put that many +1/+1 counters on this creature.
Cycling {2} ({2}, Discard this card: Draw a card.)

Cryptcaller Chariot

Menace
Whenever you discard one or more cards, create that many tapped 2/2 black Zombie creature tokens.
Crew 2

Green Goblin

Flying, menace
Spells you cast from your graveyard cost {2} less to cast.
Goblin Formula — Each nonland card in your graveyard has mayhem. The mayhem cost is equal to its mana cost. (You may cast a card from your graveyard for its mayhem cost if you discarded it this turn. Timing rules still apply.)

Norman Osborn

Norman Osborn can't be blocked.
Whenever Norman Osborn deals combat damage to a player, he connives. (Draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on this creature.)
{1}{U}{B}{R}: Transform Norman Osborn. Activate only as a sorcery.

Norman Osborn // Green Goblin

Surly Badgersaur

Whenever you discard a creature card, put a +1/+1 counter on this creature.
Whenever you discard a land card, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")
Whenever you discard a noncreature, nonland card, this creature fights up to one target creature you don't control.

Lazotep Chancellor

Whenever you discard a card, you may pay {1}. If you do, amass Zombies 2. (Put two +1/+1 counters on an Army you control. It's also a Zombie. If you don't control an Army, create a 0/0 black Zombie Army creature token first.)

Monument to Endurance

Whenever you discard a card, choose one that hasn't been chosen this turn —
• Draw a card.
• Create a Treasure token.
• Each opponent loses 3 life.

Captain Howler, Sea Scourge

Ward—{2}, Pay 2 life.
Whenever you discard one or more cards, target creature gets +2/+0 until end of turn for each card discarded this way. Whenever that creature deals combat damage to a player this turn, you draw a card.

Magmakin Artillerist

Whenever you discard one or more cards, this creature deals that much damage to each opponent.
Cycling {1}{R} ({1}{R}, Discard this card: Draw a card.)
When you cycle this card, it deals 1 damage to each opponent.

Fluctuator

Cycling abilities you activate cost {2} less to activate.

Hobgoblin, Mantled Marauder

Flying, haste
Whenever you discard a card, Hobgoblin gets +2/+0 until end of turn.

Mystic Redaction

At the beginning of your upkeep, scry 1.
Whenever you discard a card, each opponent mills two cards. (They put the top two cards of their library into their graveyard.)

Cool but Rude

(Gain the next level as a sorcery to add its ability.)
Whenever you attack, you may discard a card. If you do, draw a card.
{1}{R}: Level 2
Whenever you discard a card, this Class deals 2 damage to each opponent.
{1}{R}: Level 3
When this Class becomes level 3, search your library for a card, put it into your hand, shuffle, then discard a card at random.