msem-instigator

At the beginning of your upkeep, you lose 1 life, then investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
Whenever you sacrifice a permanent, each opponent loses 1 life.

At the beginning of your upkeep, if an opponent has more life than you, create a 4/4 red Elemental creature token with haste and “Creatures blocking this creature have winnow.” (Damage dealt to a creature with winnow causes its controller to lose that much life.)

When Ritesinger Shaman dies, each player discards a card.

As Ritual Preparations enters, choose a color.
You don't lose unspent mana of the chosen color as steps and phases end.

({T}: Add {U} or {R}.)
As Ritzy Parlor enters, you may pay {1}. If you don't, Ritzy Parlor enters tapped.

{T}, Pay 1 life: Add {W}.
{6}{W}{W}{W}, Exile Rius, Temple of the Grandfather from your hand: Target player gains 20 life.

Riv's Safehouse enters tapped.
When Riv's Safehouse enters, you may mill two cards.
{T}: Add {U} or {B}.

Menace
Sabotage — Whenever an opponent or permanent an opponent controls becomes the target of a spell you control, each opponent discards a card.

Flying

When River Miscreants enters, target creature you control can't be blocked this turn.
{2}{U}: Return River Miscreants to its owner's hand. Activate only as a sorcery.

{1}, {T}: You gain 1 life.
{2}, {T}: Tap target creature.

{U}, {T}: You may tap or untap another target creature.
Whenever one or more other creatures you control deal combat damage to a player, you may untap Riverchase Diver.

Harmony — Untap target permanent.
Whenever you cast an instant or sorcery spell, harmonize. (Trigger up to one harmony of one permanent you control.)

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

Flying
Whenever Rivha and at least two other creatures attack, exile all other attacking creatures you control. For each creature exiled this way, create a 3/3 white Angel creature token with flying that's tapped and attacking.

When Rixia, Rift Shunted enters, target creature can't be blocked this turn.
Whenever a creature you control deals combat damage to an opponent, you may aetherize it. (To aetherize, create a token that's a copy of it, then exile that token.)

As Road to Alratha enters, choose near or far.
Whenever you attack,
• Near — Creatures you control get +1/+1 until end of turn.
• Far — Put a +1/+1 counter on target creature you control. Untap it.

{2}, {T}: Tap target creature.

First strike
Whenever a creature dealt damage by Roadside Reaper this turn dies, you may discard a card. If you do, put a +1/+1 counter on Roadside Reaper and draw a card.

You may play this card transformed.
Trample

Trample
Chosen one ({W}{U}{B}{R}{G}: Transform this permanent.)

Flying
Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)

Flash
Enchant creature
When Roar of the Wilds enters, enchanted creature gets +3/+3 until end of turn.
When enchanted creature dies, create a 1/1 green Saproling creature token.

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

{1}{R}: Roaring Dracowyrm gets +2/+0 until end of turn. Activate only once each turn.