River's Grasp

If {U} was spent to cast this spell, return up to one target creature to its owner's hand. If {B} was spent to cast this spell, target player reveals their hand, you choose a nonland card from it, then that player discards that card. (Do both if {U}{B} was spent.)

Swamp

River Kelpie

Whenever this creature or another permanent enters from a graveyard, draw a card.
Whenever a player casts a spell from a graveyard, draw a card.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Biting Tether

Enchant creature
You control enchanted creature.
At the beginning of your upkeep, put a -1/-1 counter on enchanted creature.

Incremental Blight

Put a -1/-1 counter on target creature, two -1/-1 counters on another target creature, and three -1/-1 counters on a third target creature.

Gnarled Effigy

{4}, {T}: Put a -1/-1 counter on target creature.

Wingrattle Scarecrow

This creature has flying as long as you control a blue creature.
This creature has persist as long as you control a black creature. (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Wanderbrine Rootcutters

This creature can't be blocked by green creatures.

Leech Bonder

This creature enters with two -1/-1 counters on it.
{U}, {Q}: Move a counter from target creature onto a second target creature. ({Q} is the untap symbol.)

Gravelgill Axeshark

Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Oona's Gatewarden

Defender, flying
Wither (This deals damage to creatures in the form of -1/-1 counters.)

Faerie Macabre

Flying
Discard this card: Exile up to two target cards from graveyards.

Inkfathom Witch

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
{2}{U}{B}: Each unblocked creature has base power and toughness 4/1 until end of turn.

Helm of the Ghastlord

Enchant creature
As long as enchanted creature is blue, it gets +1/+1 and has "Whenever this creature deals damage to an opponent, draw a card."
As long as enchanted creature is black, it gets +1/+1 and has "Whenever this creature deals damage to an opponent, that player discards a card."

Gloomlance

Destroy target creature. If that creature was green or white, its controller discards a card.

Trip Noose

Wasp Lancer

Torture

Enchant creature
{1}{B}: Put a -1/-1 counter on enchanted creature.

Island

Chainbreaker

This creature enters with two -1/-1 counters on it.
{3}, {T}: Remove a -1/-1 counter from target creature.

Loch Korrigan

{U/B}: This creature gets +1/+1 until end of turn.

Grim Poppet

This creature enters with three -1/-1 counters on it.
Remove a -1/-1 counter from this creature: Put a -1/-1 counter on another target creature.

Scarscale Ritual

As an additional cost to cast this spell, put a -1/-1 counter on a creature you control.
Draw two cards.