Aether Flash

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

Repercussion

Whenever a creature is dealt damage, Repercussion deals that much damage to that creature's controller.

Gideon of the Trials

+1: Until your next turn, prevent all damage target permanent would deal.
0: Until end of turn, Gideon of the Trials becomes a 4/4 Human Soldier creature with indestructible that's still a planeswalker. Prevent all damage that would be dealt to him this turn.
0: You get an emblem with "As long as you control a Gideon planeswalker, you can't lose the game and your opponents can't win the game."

Humility

All creatures lose all abilities and have base power and toughness 1/1.

Powerstone Minefield

Whenever a creature attacks or blocks, Powerstone Minefield deals 2 damage to it.

Academy Rector

When Academy Rector dies, you may exile it. If you do, search your library for an enchantment card, put that card onto the battlefield, then shuffle.

Magus of the Balance

{4}{W}, {T}, Sacrifice Magus of the Balance: Each player chooses a number of lands they control equal to the number of lands controlled by the player who controls the fewest, then sacrifices the rest. Players discard cards and sacrifice creatures the same way.

Caltrops

Whenever a creature attacks, Caltrops deals 1 damage to it.

Greater Auramancy

Other enchantments you control have shroud. (A permanent with shroud can't be the target of spells or abilities.)
Enchanted creatures you control have shroud.

Narset, Enlightened Master

First strike, hexproof
Whenever Narset, Enlightened Master attacks, exile the top four cards of your library. Until end of turn, you may cast noncreature spells from among those cards without paying their mana costs.