Sentinel's Mark

Flash
Enchant creature
Enchanted creature gets +1/+2 and has vigilance.
Addendum — When this Aura enters, if you cast it during your main phase, enchanted creature gains lifelink until end of turn.

Ravager Wurm

Riot (This creature enters with your choice of a +1/+1 counter or haste.)
When this creature enters, choose up to one —
• This creature fights target creature you don't control.
• Destroy target land with an activated ability that isn't a mana ability.

Rhythm of the Wild

Creature spells you control can't be countered.
Nontoken creatures you control have riot. (They enter with your choice of a +1/+1 counter or haste.)

Rubblebelt Runner

This creature can't be blocked by creature tokens.

Savage Smash

Target creature you control gets +2/+2 until end of turn. It fights target creature you don't control. (Each deals damage equal to its power to the other.)

Senate Guildmage

{W}, {T}: You gain 2 life.
{U}, {T}: Draw a card, then discard a card.

Spirit

Seraph of the Scales

Flying
{W}: This creature gains vigilance until end of turn.
{B}: This creature gains deathtouch until end of turn.
Afterlife 2 (When this creature dies, create two 1/1 white and black Spirit creature tokens with flying.)

Sharktocrab

{2}{G}{U}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on this creature, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Simic Ascendancy

{1}{G}{U}: Put a +1/+1 counter on target creature you control.
Whenever one or more +1/+1 counters are put on a creature you control, put that many growth counters on this enchantment.
At the beginning of your upkeep, if this enchantment has twenty or more growth counters on it, you win the game.

Sphinx of New Prahv

Flying, vigilance
Spells your opponents cast that target this creature cost {2} more to cast.

Sphinx's Insight

Draw two cards.
Addendum — If you cast this spell during your main phase, you gain 2 life.

Sky Tether

Enchant creature
Enchanted creature has defender and loses flying.

Sunder Shaman

This creature can't be blocked by more than one creature.
Whenever this creature deals combat damage to a player, destroy target artifact or enchantment that player controls.

Syndicate Guildmage

{1}{W}, {T}: Tap target creature with power 4 or greater.
{4}{B}, {T}: This creature deals 2 damage to target opponent or planeswalker.

Teysa Karlov

If a creature dying causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.
Creature tokens you control have vigilance and lifelink.

Theater of Horrors

At the beginning of your upkeep, exile the top card of your library.
During your turn, if an opponent lost life this turn, you may play lands and cast spells from among cards exiled with this enchantment.
{3}{R}: This enchantment deals 1 damage to target opponent or planeswalker.

Ravnica Allegiance