msem-instigator

{3}: Sellsword Contraption becomes the creature type of your choice until end of turn.

Whenever a quest counter is put on a permanent you control, upgrade Selvar, the Seeker. (Give it one of the listed counters it doesn't already have.)
• +1/+1
• First strike
• Vigilance
• Reach
• Trample
• Lifelink

Death knell — Put a +1/+1, flying, lifelink, or menace counter on Senn, the Haunting Gaze, then trigger a death knell of another permanent you control. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)

Lionize {1}{W} ({1}{W}, Exile this card from your hand: Put a +1/+1 counter on target creature and it gains the following ability until end of turn. You may cast this card on a later turn from exile.)
Flying

Reach, ward {3}

Soldiercycling {1}{W}, Wizardcycling {1}{U}, Zombiecycling {1}{B}, Warriorcycling {1}{R}, Elfcycling {1}{G} ({1}{G}, Discard this card: Search your library for an Elf card, reveal it, and put it into your hand, then shuffle.)
Sentinel of Latter Days is every creature type as long as it's in your library.

Deathtouch
{U/B}: Change a target of target spell or ability that targets Serafina to another creature you control.
Whenever Serafina deals damage to a player, at the beginning of the next end step, that player loses life equal to the life they lost this turn.

Serene Hart can't be blocked by creatures with power 4 or greater.

Defender (This creature can't attack.)
Whenever you cast a spell, if it isn't your main phase, Serene Meditant loses defender until the beginning of your next end step.

Menace
Servitor Vanguard gets +X/+X, where X is the number of other artifacts you control.

Menace
When Setar Ritualist enters or whenever you cast a spell, if {U}{R} was spent to cast it, Setar Ritualist deals 3 damage to target permanent, then tap that permanent. Put a +1/+1 counter on Setar Ritualist.

Heroic — Whenever you cast a spell that targets Setessan Avenger, create a 1/1 green Nymph Dryad enchantment creature token with “{T}: Add {G}.”
Whenever Setessan Avenger deals combat damage to a player, untap all lands and Dryads you control.

When Sewer Dweller enters or dies, create a 1/1 black Rat creature token with “This creature can't block.”

Transcend (Activate as a sorcery to gain the next type and a +1/+1 counter.)
Ward {2}
{2}{U}: Demigod — Exchange a card in your hand and a noncreature, nonland card in your graveyard.
{6}{U}: God — Exchange control of two target permanents that share a card type.

When Sha'Iv's Scout enters, adjudicate. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)
Whenever an Aura you control enters, target creature can't block this turn.

When Shadowstrider dies, create a 2/2 colorless Spirit creature token.

Haste
Whenever Shala's Phantasm attacks, you may sacrifice a creature. If you do, Shala's Phantasm deals 3 damage to any target.

When Shaman of Burning Ashes enters, return target instant or sorcery card from your graveyard to your hand. When you do, each opponent loses X life, where X is that card's mana value.

When Shambling Gutless enters, target player discards a card.

When Shark Slayer enters, you may destroy target creature with mana value less than or equal to the number of artifacts you control.

Flying
When Sharp-Eyed Wingmate enters, you may return target creature to its owner's hand.

Lifelink
Each other artifact creature you control enters with an additional +1/+1 counter on it.

When Shawlbinder enters, if you control a Desert, exile another target permanent. Return that card to the battlefield under its owner's control at the beginning of the next end step.

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you casting a noncreature spell causes an ability of a creature you control to trigger, that creature gains your choice of first strike, haste, menace, or trample until end of turn.

Vigilance
Whenever one or more creatures you control deals combat damage to a player, you may discard a card. If you do, create a Function token with “Draw two cards.” (It's an enchantment. As you cast an instant or sorcery spell, sacrifice any number of Functions to add their effects to that spell.)