Deceiver Exarch

Flash (You may cast this spell any time you could cast an instant.)
When this creature enters, choose one —
• Untap target permanent you control.
• Tap target permanent an opponent controls.

Pestermite

Flash
Flying
When this creature enters, you may tap or untap target permanent.

Coercive Recruiter

Whenever this creature or another Pirate you control enters, gain control of target creature until end of turn. Untap that creature. Until end of turn, it gains haste and becomes a Pirate in addition to its other types.

Bounding Krasis

Flash (You may cast this spell any time you could cast an instant.)
When this creature enters, you may tap or untap target creature.

Loot, the Pathfinder

Double strike, vigilance, haste
Exhaust — {G}, {T}: Add three mana of any one color. (Activate each exhaust ability only once.)
Exhaust — {U}, {T}: Draw three cards.
Exhaust — {R}, {T}: Loot deals 3 damage to any target.

Reptilian Recruiter

Trample
When this creature enters, choose target creature. If that creature's power is 2 or less or if you control another Lizard, gain control of that creature until end of turn, untap it, and it gains haste until end of turn.

Captain of the Mists

Whenever another Human you control enters, untap this creature.
{1}{U}, {T}: You may tap or untap target permanent.

Corridor Monitor

When this creature enters, untap target artifact or creature you control.

Hyrax Tower Scout

When this creature enters, untap target creature.

Breaching Hippocamp

Flash (You may cast this spell any time you could cast an instant.)
When this creature enters, untap another target creature you control.

Splinter Twin

Enchant creature
Enchanted creature has "{T}: Create a token that's a copy of this creature, except it has haste. Exile that token at the beginning of the next end step."

Zealous Conscripts

Haste
When this creature enters, gain control of target permanent until end of turn. Untap that permanent. It gains haste until end of turn.