msem-instigator

{T}, Sacrifice Rickety Guildhall: Search your library for a Forest or Island card and put it onto the battlefield tapped, then shuffle.

Whenever you cast a nonblue spell, create a 1/0 blue Horse Nymph creature token.
Horses get +1/+1 and have flying.

Primal {R} (During your turn, you may cast this spell for {R} instead of playing a land.)
Target creature gets +4/+0 and gains trample until end of turn.

Enchant creature
Enchanted creature has “At the beginning of each player's end step, that player chooses another creature they control. That creature fights enchanted creature.”

First strike
Engage (This creature must be blocked each combat if able.)

Vanishing 3 (This permanent enters with three time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
When the last time counter is removed from Rising Riots, destroy target land.

River's Wrath deals 2 damage to any target. If you've been dealt damage this turn, River's Wrath deals 4 damage instead.

When Rotting Sunseeker dies, return target creature card with power 2 or less from your graveyard to your hand.

{T}: Add {B} or {G}. You lose 1 life.

{T}, Sacrifice Ruined Citadel: Search your library for a Mountain or Plains card and put it onto the battlefield tapped, then shuffle.

Enchant creature
Enchanted creature gets +3/+0 and has menace.
Whenever enchanted creature deals combat damage to a player, discard a card, then draw a card.

Whenever you gain life, target opponent loses that much life.

Up to three target creatures each get +1/+1 until end of turn.

Whenever one or more nontoken Merfolk you control attack, create a 2/1 red Merfolk creature token.

Indestructible
Whenever a creature an opponent controls dies, put five +1/+1 counters on Scion of Death.

{2}{W}, {T}: Target creature gets +2/+2 and gains first strike until end of turn.

Primal {3}{U}{U} (During your turn, you may cast this spell for {3}{U}{U} instead of playing a land.)
Draw a card for each land you control, then discard that many cards unless this spell was cast for its primal cost.

At the beginning of your upkeep, you gain 1 life. Then if your life total is greater than or equal to your starting life total, you gain an additional 1 life and scry 1. Then if your life total is greater than or equal to three times your starting life total, you win the game.

{T}: Add {R} or {W}.
{R}{W}, {T}: Target creature gains first strike and haste until end of turn.

Primal {W} (During your turn, you may cast this spell for {W} instead of playing a land.)
Destroy target attacking or blocking creature.

Deathtouch
Cards can't leave graveyards.
If a creature would die, you may pay {X}, where X is the number of cards in your graveyard. If you do, instead exile it, then return that card to the battlefield under your control.

Reveal the top five cards of your library. Put one of those cards into your hand. Target opponent chooses two of those cards. Exile the chosen cards, then put the rest into your hand.

{T}, Sacrifice Serene Trail: Search your library for a Forest or Plains card and put it onto the battlefield tapped, then shuffle.

Destroy target token.

Other creatures you control get +0/+1.
Whenever a creature you control perseveres, you gain 1 life. (A creature perseveres when it survives damage.)