Harsh Mentor

Whenever an opponent activates an ability of an artifact, creature, or land on the battlefield, if it isn't a mana ability, Harsh Mentor deals 2 damage to that player.

Aether Flash

Whenever a creature enters the battlefield, Aether Flash deals 2 damage to it.

Widespread Panic

Whenever a spell or ability causes its controller to shuffle their library, that player puts a card from their hand on top of their library.

Torbran, Thane of Red Fell

If a red source you control would deal damage to an opponent or a permanent an opponent controls, it deals that much damage plus 2 instead.

Stranglehold

Your opponents can't search libraries.
If an opponent would begin an extra turn, that player skips that turn instead.

Brand of Ill Omen

Enchant creature
Cumulative upkeep {R} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Enchanted creature's controller can't cast creature spells.

Treasure Nabber

Whenever an opponent taps an artifact for mana, gain control of that artifact until the end of your next turn.