Whenever a Subroutine you control enters, you may pay {2}. If you do, it runs.
Whenever a Subroutine you control runs, this creature gets +1/+1 until end of turn.

When Scruffy Rascal enters, mill three cards. You may put a permanent card from among the cards milled this way into your hand. If you don't, create a Treasure token.

Flow — {4}{W}: Create a tapped 0/0 colorless Golem artifact creature token with “This creature gets +1/+1 for each artifact you control.”

Scuttle Tank enters with a defender counter on it.

Surface {U}. Scuttling Cicada surfaces transformed.

When Sea Breeze enters, return up to one target creature to its owner's hand, then surveil 1.

When Seafloor Scavenger enters or deals combat damage to a player, you may return target exiled card with surface you own to your hand.

Look at the top two cards of your library. Put one into your hand and the other into your graveyard.
Surface {2}{U}

Flash
When Seal Away enters, exile target tapped creature an opponent controls until Seal Away leaves the battlefield.

At the beginning of each end step, create a 2/2 white and blue Seal Orb creature token if you activated two or more nonmana abilities this turn.
{W}{U}: Scry 1. You gain 1 life.

When this enchantment enters, exile target nonland permanent an opponent controls until this enchantment leaves the battlefield.
Cycling {2}

Target player reveals their hand. You may choose a nonland card from it. If you do, that player discards that card. Otherwise, draw a card.

This spell costs {2} less to cast if you've activated a nonmana ability this turn.
Searing Grace deals 3 damage to any target.

Vigilance
When Seasoned Spymaster enters, teach target creature vigilance.

Lifelink
Whenever Secluded Gorgon dies, you may bless target creature.

Secluded Hangar enters tapped unless you control a basic non-Forest land.
{T}: Add {G}.
{2}, {T}: Put a +1/+1 counter on target creature that entered this turn.

Exile all creatures you don't control. Then return those cards to the battlefield tapped under their owners' control unless you've cast another spell named Second Crown's Fall this game. Then exile Second Crown's Fall.

Whenever this enchantment or another nonland, nontoken permanent you control enters, if it wasn't cast, draw a card. You may put a land card from your hand onto the battlefield tapped.
Creatures you control with power or toughness 1 or less can't be blocked.

Flash
When Security Initiative enters, you may tap or untap target nonland permanent. Then draw a card.
An opponent controls three or more tapped nonland permanents.

Flying
Whenever Seeker Orbs becomes tapped, scry 1.

Whenever a Forest you control enters, put a +1/+1 counter on Seeker of New Horizons. Then you may remove four +1/+1 counters from among creatures you control. If you do, bless that land.

Whenever a land you control enters, scry 1. If that land is a Ruin, scry 2 instead.

As an additional cost to cast this spell, exile three or more creature cards with different names from your graveyard.
Whenever this creature attacks, defending player chooses a card exiled with it. Put that card onto the battlefield under your control.

When Seer of the Aspirants enters, surveil 1.
Wander {2}{G}

Haste
Mountaincycling {2}