Sliptide Serpent

{3}{U}: Return Sliptide Serpent to its owner's hand.

Wormhole Serpent

{3}{U}: Target creature can't be blocked this turn.

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.)

Seasonal Ritual

Add one mana of any color. (Then exile this card. You may cast the creature later from exile.)

Rosethorn Acolyte

Rosethorn Acolyte // Seasonal Ritual

Cryptic Serpent

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.

Springbloom Druid

When this creature enters, you may sacrifice a land. If you do, search your library for up to two basic land cards, put them onto the battlefield tapped, then shuffle.

Brightwood Tracker

{5}{G}, {T}: Look at the top four cards of your library. You may reveal a creature card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Wildwood Tracker

Whenever Wildwood Tracker attacks or blocks, if you control another non-Human creature, Wildwood Tracker gets +1/+1 until end of turn.

Maraleaf Rider

Sacrifice a Food: Target creature blocks Maraleaf Rider this turn if able.

Frilled Sea Serpent

{5}{U}{U}: Frilled Sea Serpent can't be blocked this turn.

Sunblade Elf

Sunblade Elf gets +1/+1 as long as you control a Plains.
{4}{W}: Creatures you control get +1/+1 until end of turn.

Shaman of Spring

When Shaman of Spring enters, draw a card.

Shoal Serpent

Defender
Landfall — Whenever a land you control enters, Shoal Serpent loses defender until end of turn.

Harbor Serpent

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Harbor Serpent can't attack unless there are five or more Islands on the battlefield.