Storm Seeker

Storm Seeker deals damage to target player equal to the number of cards in that player's hand.

Paupers' Cage

At the beginning of each opponent's upkeep, if that player has two or fewer cards in hand, this artifact deals 2 damage to that player.

Lavaborn Muse

At the beginning of each opponent's upkeep, if that player has two or fewer cards in hand, this creature deals 3 damage to that player.

Champions of Minas Tirith

When this creature enters, you become the monarch.
At the beginning of combat on each opponent's turn, if you're the monarch, that opponent may pay {X}, where X is the number of cards in their hand. If they don't, they can't attack you this combat.

Realm Seekers

This creature enters with X +1/+1 counters on it, where X is the total number of cards in all players' hands.
{2}{G}, Remove a +1/+1 counter from this creature: Search your library for a land card, reveal it, put it into your hand, then shuffle.

Search Warrant

Target player reveals their hand. You gain life equal to the number of cards in that player's hand.

Multani, Maro-Sorcerer

Shroud (This creature can't be the target of spells or abilities.)
Multani's power and toughness are each equal to the total number of cards in all players' hands.

The Second Doctor

Players have no maximum hand size.
How Civil of You — At the beginning of your end step, each player may draw a card. Each opponent who does can't attack you or permanents you control during their next turn.

Wolfcaller's Howl

At the beginning of your upkeep, create X 2/2 green Wolf creature tokens, where X is the number of your opponents with four or more cards in hand.

Clara Oswald

Impossible Girl — If Clara Oswald is your commander, choose a color before the game begins. Clara Oswald is the chosen color.
If a triggered ability of a Doctor you control triggers, that ability triggers an additional time.
Doctor's companion (You can have two commanders if the other is the Doctor.)

Sword of War and Peace

Equipped creature gets +2/+2 and has protection from red and from white.
Whenever equipped creature deals combat damage to a player, this Equipment deals damage to that player equal to the number of cards in their hand and you gain 1 life for each card in your hand.
Equip {2}