Merfolk of the Depths

Activated abilities of artifacts your opponents control can't be activated. +1: Until your next turn, up to one target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value. −2: You may reveal an artifact card you own from outside the game or choose a face-up artifact card you own in exile. Put that card into your hand.

Whenever a creature you control attacks alone, it gets +X/+X until end of turn, where X is the number of creatures you control.

This creature has vigilance as long as you control a Gate.

Target creature gets +2/+2 until end of turn. Addendum — If you cast this spell during your main phase, that creature gains flying until end of turn.

When this creature enters, detain target creature an opponent controls. (Until your next turn, that creature can't attack or block and its activated abilities can't be activated.)

When this creature enters, detain up to two target creatures your opponents control. (Until your next turn, those creatures can't attack or block and their activated abilities can't be activated.)

Defender Extort (Whenever you cast a spell, you may pay W/B. If you do, each opponent loses 1 life and you gain that much life.)

Flying Creatures can't attack you.