msem-instigator

If you would create an Army token while Mehr's Unending Horde is in your graveyard, you may instead return Mehr's Unending Horde from your graveyard to the battlefield.
Counters remain on Mehr's Unending Horde as it moves to any zone other than a player's hand or library.

Flying
Menagerie — At the beginning of combat on your turn, if there are five or more creature types among creatures you control, create a 1/1 black Insect Spirit creature token with flying and you gain 1 life.

Living weapon (When this Equipment enters, create a 0/0 black Phyrexian Germ creature token, then attach this to it.)
Equipped creature gets +1/-1.
Whenever equipped creature dies, draw a card. This ability triggers only once each turn.
Equip {1}

Whenever Sporecaster or another Insect you control enters, each opponent loses 1 life.

Desecrate (When this creature enters, you may sacrifice an artifact or land.)
When Beastback Raider desecrates a permanent, discard your hand, then draw three cards.

Sacrifice a creature: Harrowing Knight gets +2/+2 until end of turn.

Target player mills four cards.
Dominance — That player mills eight cards instead if you control the creature with the greatest power or tied for the greatest power.

When Elvish Skyranger enters, search your library for a card with a basic land type, put it onto the battlefield tapped, then shuffle.

Shock Blast deals X damage to target creature, where X is the number of instant and sorcery cards in your graveyard.

Cadence (Whenever you cast a spell, if its mana value is greater than this creature's power, put a +1/+1 counter on this creature.)
When Painwield Explorer dies, it deals damage equal to its power to target player or planeswalker.

Harvest (You may tap any number of creatures you control as you cast this spell. If you do, reduce this spell's mana cost by their total power.)
Search your library for a creature card with mana value X or less and put it onto the battlefield. Then shuffle.

When Ikari-no-Oni enters, other creatures you control get +1/+0 until end of turn.

Flying
Whenever a player shuffles their library, Steamquiver Strix deals 2 damage to that player.

{4}, {T}: Look at the top card of your library. If it's a land card, you may put it onto the battlefield tapped. If you don't put the card onto the battlefield, put it into your hand.

Choose two target creatures controlled by different players. Return those creatures to their owners' hands.

Flying, haste
{R}: Varagan Wyrmling gets +1/+0 until end of turn. Activate this ability only up to three times each turn.

Flying (This creature can't be blocked except by creatures with flying or reach.)

During your opponents' turns, Chroma, the Faerie Circle has all basic land types in all zones.
Chroma, the Faerie Circle enters tapped.

Flying
When Sky-Torrent Navigator enters, forebode. If you control two or more Pirates, forebode again. (To forebode, create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)

Haste
Whenever Arpechian Tiger attacks, you may sacrifice a land. If you do, Arpechian Tiger deals 3 damage to target creature or planeswalker.

Create three 1/1 white Soldier creature tokens.
Soldiercycling {2}{W} ({2}{W}, Discard this card: Search your library for a Soldier card, reveal it, and put it into your hand, then shuffle.)

Trial 4 (As you cast this spell, an opponent of your choice may pay 4 life. If they don't, they fail the trial.)
When Treacherous Devil enters, if an opponent passed the trial, that player gains control of Treacherous Devil.

{1}, {T}, Move a -1/-1 counter from another creature onto Fervent Arbiter: Exile target creature you don't control until Fervent Arbiter leaves the battlefield.

[+1]: Until end of turn, All-Enduring Mafua becomes a 5/5 Cat Warrior creature with lifelink and indestructible. (He doesn't lose loyalty while he's not a planeswalker.)
[–2]: Exile target creature.
[–X]: Return each creature card with mana value X from your graveyard to your hand.

Rugged Highlands enters tapped.
When Rugged Highlands enters, you gain 1 life.
{T}: Add {R} or {G}.