msem-instigator

Flying, menace
When Riftkeeper Entity enters the battlefield, discard your hand, then draw cards equal to the number of differently named lands you control.
{1}{R}, Discard Riftkeeper Entity: Create a tapped colorless land token named Fading Rift with “{T}, Sacrifice this land: Add one mana of any color.”

Put a +1/+1 counter on up to one target creature.
Draw a card.

At the beginning of your end step, aetherize target permanent you control. (To aetherize, create a token that's a copy of it, then exile that token.)

Flash
When Rippling Water Arcanist enters the battlefield, copy target instant or sorcery spell you control, then return it to its owner's hand. You may choose new targets for the copy.

Enchant creature
When Rising Tides enters the battlefield, draw a card.
At the beginning of each upkeep, if enchanted creature is untapped, tap it.

{7}{U}: Tap up to three target nonland permanents. This ability costs {2} less to activate if you control a legendary creature.

({T}: Add {U} or {R}.)
Roaring Cascade enters the battlefield tapped.

At the beginning of combat on each of your turns, you may sacrifice a land or exile a land card from your graveyard. If you do, create two 1/1 red Goblin creature tokens with haste. Exile those tokens at the beginning of the next end step.

Legendary creatures you control have hexproof.

Pay 3 life: Put a +1/+1 counter on target creature.

When Rootbound Awakener enters the battlefield, create a green Aura enchantment token named Vivification attached to target creature or land. The token has enchant creature or land and “Enchanted permanent is a creature with base power and toughness 5/5 in addition to its other types.”

When Rootwarper enters the battlefield, you may sacrifice a land. If you do, search your library for a land card, put that card onto the battlefield tapped, then shuffle.

When Rubble Seer enters the battlefield, you may sacrifice a land or exile a land card from your graveyard. If you do, exile the top card of your library. Until the end of your next turn, you may play that card.

({T}: Add {R}, {G}, or {W}.)
Rugged Dominion enters the battlefield tapped.

Menace
When Ruin Delver enters the battlefield, you may sacrifice a land or exile a land card from your graveyard. If you do, you draw a card and you lose 1 life. Repeat this process once.

Flying
When Rushwater Hunter enters the battlefield, you may return target creature to its owner's hand.

Improve {1}{U} ({1}{U}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
At the beginning of your end step, if one or more embattled creatures you controlled dealt damage to a player, you may draw a card. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Haste
Whenever an embattled creature you control deals combat damage to a player, you may pay {2}{G}. If you do, create a token that's a copy of that creature, except the token isn't legendary if the creature is legendary. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

When Ryleth, Vengeful Shadow enters the battlefield, create two 1/1 green Elf creature tokens.
Whenever you attack, you may pay {1}{B/G}. When you do, return target creature card with mana value less than or equal to the number of attacking creature tokens you control to the battlefield tapped and attacking.

Flying
Legendary spells you cast cost {1} less to cast.
{W}{U}{B}{R}{G}: Search your library or graveyard for a legendary card, reveal that card, and put it into your hand. If you searched your library this way, shuffle.

Create a token that's a copy of a creature token you control.
Draw a card.

Sacred Summits enters the battlefield tapped.
{T}: Add one mana of any color among the color identity of legendary creatures and planeswalkers you control or legendary cards in your command zone.

When Saddled Scuttleback enters the battlefield, you may search your library for a Crab, Fish, Jellyfish, Kraken, Leviathan, Merfolk, Nautilus, Octopus, Otter, Oyster, Pirate, Seal, Serpent, Shark, Shrimp, Sponge, Squid, Starfish, Trilobite, Turtle, Whale, or Island card, reveal it, put it into your hand, then shuffle.

Trample
When Saddlesaur Guide enters the battlefield, create a green Aura enchantment token named Hefty Load attached to target creature. The token has enchant creature and “Enchanted creature gets +2/+2 and has trample.”

Flying, prowess
Once each turn, when you cast a noncreature spell, you may create a 4/4 blue Sphinx Wizard creature token with flying, then scry 1.
{2}{U}{U}, Discard Sage of the Hereafter: Create a 4/4 blue Sphinx Wizard creature token with flying, then scry 1. Activate only as a sorcery.