Counterspell

Lingering Souls

Create two 1/1 white Spirit creature tokens with flying.
Flashback {1}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Geist of Saint Traft

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Whenever Geist of Saint Traft attacks, create a 4/4 white Angel creature token with flying that's tapped and attacking. Exile that token at end of combat.

Abuelo, Ancestral Echo

Flying, ward {2}
{1}{W}{U}: Exile another target creature or artifact you control. Return it to the battlefield under its owner's control at the beginning of the next end step.

Anafenza, Kin-Tree Spirit

Whenever another nontoken creature you control enters, bolster 1. (Choose a creature with the least toughness among creatures you control and put a +1/+1 counter on it.)

Counterflux

This spell can't be countered.
Counter target spell you don't control.
Overload {1}{U}{U}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Slip Out the Back

Put a +1/+1 counter on target creature. It phases out. (Treat it and anything attached to it as though they don't exist until its controller's next turn.)

Ayumi, the Last Visitor

Legendary landwalk (This creature can't be blocked as long as defending player controls a legendary land.)

Countersquall

Counter target noncreature spell. Its controller loses 2 life.

Hindering Light

Counter target spell that targets you or a permanent you control.
Draw a card.

Mox Amber

{T}: Add one mana of any color among legendary creatures and planeswalkers you control.

Agrus Kos, Spirit of Justice

Double strike, vigilance
Whenever Agrus Kos, Spirit of Justice enters or attacks, choose up to one target creature. If it's suspected, exile it. Otherwise, suspect it. (A suspected creature has menace and can't block.)

Absorb

Rewind

Counter target spell. Untap up to four lands.

Azorius Herald

Azorius Herald can't be blocked.
When Azorius Herald enters, you gain 4 life.
When Azorius Herald enters, sacrifice it unless {U} was spent to cast it.