msem-instigator

Target creature gets -2/-2 until end of turn.
{3}{B}, Exile Rift Splicing from your graveyard: Aetherize target creature card with mana value 3 or less in a graveyard. Activate only as a sorcery. (To aetherize, create a token that's a copy of it, then exile that token.)

Wanderlust — When Riftbreaker Mage dies, if you control four or more differently named lands, Riftbreaker Mage deals damage equal to its power to each opponent.

Flying, menace
When Riftkeeper Entity enters, 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.”

{T}: Add {C}.
{3}, {T}: Add {C} for each basic land you control.

Rilken Forcefield Keeper gets +1/+1 for each enchantment you control.
Sacrifice Rilken Forcefield Keeper: Exile target permanent you control. Return that card to the battlefield under your control at the beginning of the next end step.

Whenever another creature you control enters, put a +1/+1 counter on it.
Whenever Rilken Preserver attacks, you may exile target nonland permanent you control, then return it to the battlefield under your control.

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.)

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.

Enchant creature
Enchanted creature can't be blocked.
Whenever enchanted creature deals combat damage to a player, you may aetherize it. (To aetherize, create a token that's a copy of it, then exile that token.)

When Rootbound Awakener enters, 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, 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, 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.

Menace
Whenever Ruin Delver attacks, 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.

{T}: Add {C}.
{4}, {T}: Look at the top two cards of your library. You may put one of them into your graveyard. Put the rest back on top in any order. If you control eight or more lands, draw a card.

When Saddled Scuttleback enters, 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, 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.”

[+2]: Exile the top two cards of your library. You may put a permanent card from among them into your hand.
[–3]: Create Salim, a legendary 3/3 green and white Cat creature token with vigilance, trample, and indestructible.
[–3]: You get an emblem with “Whenever a creature you control enters, that creature gets +2/+2 and gains haste until end of turn.”

Menace
When Scion of Calamities enters, exile the top two cards of your library. Until the end of your next turn, you may play one of those cards.
Whenever a Mountain you control enters, you may aetherize Scion of Calamities. (To aetherize, create a token that's a copy of it, then exile that token.)

Deathtouch
When Scion of Desolation enters, put target creature card with mana value 3 or less from a graveyard onto the battlefield under your control.
Whenever a Swamp you control enters, you may aetherize Scion of Desolation. (To aetherize, create a token that's a copy of it, then exile that token.)

Trample
When Scion of Flourishing enters, put a +1/+1 counter on each other creature you control. Those creatures gain trample until end of turn.
Whenever a Forest you control enters, you may aetherize Scion of Flourishing. (To aetherize, create a token that's a copy of it, then exile that token.)

Vigilance
When Scion of Storms enters, create a 2/2 white Elemental creature token with flying.
Whenever a Plains you control enters, you may aetherize Scion of Storms. (To aetherize, create a token that's a copy of it, then exile that token.)

Flying
When Scion of Torrents enters, you may return target nonland permanent to its owner's hand.
Whenever an Island you control enters, you may aetherize Scion of Torrents. (To aetherize, create a token that's a copy of it, then exile that token.)

When Sealed Riftway enters, exile up to one target card from a graveyard.
{2}, {T}, Sacrifice Sealed Riftway: Exile target player's graveyard. Draw a card.

Trample
When Sealer of Pacts enters, sacrifice any number of permanents, then draw that many cards.

Sabotage — Whenever an opponent or permanent an opponent controls becomes the target of a spell you control, target creature you control can't be blocked this turn.
{B}{B}{B}: Secret Thief gets +3/+0 until end of turn.