Spiny Starfish

{U}: Regenerate Spiny Starfish.
At the beginning of each end step, if Spiny Starfish regenerated this turn, create a 0/1 blue Starfish creature token for each time it regenerated this turn.

Leechridden Swamp

({T}: Add {B}.)
Leechridden Swamp enters tapped.
{B}, {T}: Each opponent loses 1 life. Activate only if you control two or more black permanents.

River's Rebuke

Return all nonland permanents target player controls to their owner's hand.

Forest

Mistford River Turtle

Whenever Mistford River Turtle attacks, another target attacking non-Human creature can't be blocked this turn.

Cold-Water Snapper

Hexproof (This creature can't be the target of spells or abilities your opponents control.)

Quagmire Lamprey

Whenever Quagmire Lamprey becomes blocked by a creature, put a -1/-1 counter on that creature.

River Kelpie

Whenever River Kelpie 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.)

Rootwater Mystic

{1}{U}: Look at the top card of target player's library.

Wandering Stream

Domain — You gain 2 life for each basic land type among lands you control.

Piranha Marsh

Piranha Marsh enters tapped.
When Piranha Marsh enters, target player loses 1 life.
{T}: Add {B}.

River Sneak

River Sneak can't be blocked.
Whenever another Merfolk you control enters, River Sneak gets +1/+1 until end of turn.

Sinister Starfish

{T}: Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Blessing of Leeches

Flash
Enchant creature
At the beginning of your upkeep, you lose 1 life.
{0}: Regenerate enchanted creature.

Lurking Crocodile

Bloodthirst 1 (If an opponent was dealt damage this turn, this creature enters with a +1/+1 counter on it.)
Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Putrid Leech

Pay 2 life: Putrid Leech gets +2/+2 until end of turn. Activate only once each turn.

Archelos, Lagoon Mystic

As long as Archelos, Lagoon Mystic is tapped, other permanents enter tapped.
As long as Archelos is untapped, other permanents enter untapped.

Mindleech Mass

Trample
Whenever Mindleech Mass deals combat damage to a player, you may look at that player's hand. If you do, you may cast a spell from among those cards without paying its mana cost.

River Bear

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Bad River

Bad River enters tapped.
{T}, Sacrifice Bad River: Search your library for an Island or Swamp card, put it onto the battlefield, then shuffle.

Underground River

{T}: Add {C}.
{T}: Add {U} or {B}. Underground River deals 1 damage to you.

Rushing River

Kicker—Sacrifice a land. (You may sacrifice a land in addition to any other costs as you cast this spell.)
Return target nonland permanent to its owner's hand. If this spell was kicked, return another target nonland permanent to its owner's hand.

Island

Woodland Stream

Woodland Stream enters tapped.
{T}: Add {G} or {U}.

Marang River Prowler

Marang River Prowler can't block and can't be blocked.
You may cast Marang River Prowler from your graveyard as long as you control a black or green permanent.

Rootwater Matriarch

{T}: Gain control of target creature for as long as that creature is enchanted.

Sigiled Starfish

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

River Boa

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
{G}: Regenerate River Boa.

You Come to a River

Choose one —
• Fight the Current — Return target nonland permanent to its owner's hand.
• Find a Crossing — Target creature gets +1/+0 until end of turn and can't be blocked this turn.

Gurmag Angler

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)

Rootwater Hunter

{T}: Rootwater Hunter deals 1 damage to any target.

Waterknot

Enchant creature
When Waterknot enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

Swamp

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.)

Blitz Leech

Flash
When Blitz Leech enters, target creature an opponent controls gets -2/-2 until end of turn. Remove all counters from that creature.

Moat Piranhas

Leech Bonder

Leech Bonder 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.)

Sygg, River Cutthroat

At the beginning of each end step, if an opponent lost 3 or more life this turn, you may draw a card. (Damage causes loss of life.)

Crocodile of the Crossing

Haste
When Crocodile of the Crossing enters, put a -1/-1 counter on target creature you control.

Stinging Lionfish

Whenever you cast your first spell during each opponent's turn, you may tap or untap target nonland permanent.

River Hoopoe

Flying
{3}{G}{U}: You gain 2 life and draw a card.

Squelching Leeches

Squelching Leeches's power and toughness are each equal to the number of Swamps you control.

Waterlogged Grove

{T}, Pay 1 life: Add {G} or {U}.
{1}, {T}, Sacrifice Waterlogged Grove: Draw a card.

River of Tears

{T}: Add {U}. If you played a land this turn, add {B} instead.

River Serpent

River Serpent can't attack unless there are five or more cards in your graveyard.
Cycling {U} ({U}, Discard this card: Draw a card.)

River Darter

River Darter can't be blocked by Dinosaurs.

Marang River Skeleton

{B}: Regenerate Marang River Skeleton.
Megamorph {3}{B} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.)