Scourge of Fleets

When this creature enters, return each creature your opponents control with toughness X or less to its owner's hand, where X is the number of Islands you control.

Sigiled Starfish

{T}: Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Thassa's Devourer

Constellation — Whenever this creature or another enchantment you control enters, target player mills two cards.

Thassa's Ire

{3}{U}: You may tap or untap target creature.

Triton Cavalry

Heroic — Whenever you cast a spell that targets this creature, you may return target enchantment to its owner's hand.

Triton Shorestalker

War-Wing Siren

Flying
Heroic — Whenever you cast a spell that targets this creature, put a +1/+1 counter on this creature.

Whitewater Naiads

Constellation — Whenever this creature or another enchantment you control enters, target creature can't be blocked this turn.

Agent of Erebos

Constellation — Whenever this creature or another enchantment you control enters, exile target player's graveyard.

Dawnbringer Charioteers

Flying, lifelink
Heroic — Whenever you cast a spell that targets this creature, put a +1/+1 counter on this creature.

Aspect of Gorgon

Enchant creature
Enchanted creature gets +1/+3 and has deathtouch. (Any amount of damage it deals to a creature is enough to destroy it.)

Bloodcrazed Hoplite

Heroic — Whenever you cast a spell that targets this creature, put a +1/+1 counter on it.
Whenever a +1/+1 counter is put on this creature, remove a +1/+1 counter from target creature an opponent controls.

Brain Maggot

When this creature enters, target opponent reveals their hand and you choose a nonland card from it. Exile that card until this creature leaves the battlefield.

Cast into Darkness

Enchant creature
Enchanted creature gets -2/-0 and can't block.

Cruel Feeding

Strive — This spell costs {2}{B} more to cast for each target beyond the first.
Any number of target creatures each get +1/+0 and gain lifelink until end of turn. (Damage dealt by a creature with lifelink also causes its controller to gain that much life.)

Dictate of Erebos

Flash
Whenever a creature you control dies, each opponent sacrifices a creature of their choice.

Journey into Nyx