Moonveil Regent

Flying
Whenever you cast a spell, you may discard your hand. If you do, draw a card for each of that spell's colors.
When Moonveil Regent dies, it deals X damage to any target, where X is the number of colors among permanents you control.

Null Brooch

{2}, {T}, Discard your hand: Counter target noncreature spell.

One with Nothing

Phyrexian Dragon Engine

Double strike
When Phyrexian Dragon Engine enters from your graveyard, you may discard your hand. If you do, draw three cards.
Unearth {3}{R}{R}
(Melds with Mishra, Claimed by Gix.)

The Deck of Many Things

{2}, {T}: Roll a d20 and subtract the number of cards in your hand. If the result is 0 or less, discard your hand.
1—9 | Return a card at random from your graveyard to your hand.
10—19 | Draw two cards.
20 | Put a creature card from any graveyard onto the battlefield under your control. When that creature dies, its owner loses the game.

Apocalypse

Exile all permanents. You discard your hand.

Jackdaw

Whenever Jackdaw deals combat damage to a player, you may discard your hand. If you do, draw a card for each artifact you control.
Crew 3

Malfegor

Flying
When Malfegor enters, discard your hand. Each opponent sacrifices a creature of their choice for each card discarded this way.

Grafted Skullcap

At the beginning of your draw step, draw an additional card.
At the beginning of your end step, discard your hand.

Avaricious Dragon

Flying
At the beginning of your draw step, draw an additional card.
At the beginning of your end step, discard your hand.

Dangerous Wager

Song of Creation

You may play an additional land on each of your turns.
Whenever you cast a spell, draw two cards.
At the beginning of your end step, discard your hand.