msem-instigator

When Moss Dweller enters, put a +1/+1 counter on another target creature.

Deathtouch

Mossvine Lurker has trample as long as it has a +1/+1 counter on it.

Vigilance, reach, trample

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)

{4}{G}: Monstrosity 2. (If this creature isn't monstrous, put two +1/+1 counters on it and it becomes monstrous.)
When Mountain Bighorn becomes monstrous, you may have it fight target creature you don't control.

Search your library for a basic land card, reveal it, put it into your hand, then shuffle.
Compose (Then if you cast this from your hand, exile it and create a Saga token with “r3—You may cast a copy of this card from exile without paying its mana cost.”)

Flash
Enchant creature
When Moved by Instinct enters, put a +1/+1 counter on enchanted creature.
Enchanted creature has haste and trample.

When Mul Daya Elder enters, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
Whenever a land you control enters, put a +1/+1 counter on Mul Daya Elder.

Exile a nonland card from your graveyard: For each colored mana symbol in that card's mana cost, add one mana of that color. Activate only once each turn. (For example, if the card's mana cost is {3}{G}{G}{W}, you add {G}{G}{W}.)

Whenever a nontoken creature you control enters, if it shares no creature types with other creatures you control, draw a card.

At the beginning of your upkeep, germinate. Then if creatures you control have total power 10 or greater, transform Mushroom Merchant. (To germinate, put a +1/+1 counter on a creature or create a 1/1 green Saproling creature token.)

Reveal cards from the top of your library until you reveal a creature card and a land card. Put those cards into your hand and the rest on the bottom of your library in a random order.
Concord — If there are four or more card types among permanents you control, create two Treasure tokens.

[+1]: Create a tapped colorless artifact token named Conch Shell with “{T}: Add one mana of any color. Spend this mana only to cast permanent spells.”
[–1]: Reveal the top X cards of your library, where X is the number of card types among permanents you control. Put a permanent card from among them into your hand and the rest into your graveyard.
[–3]: Create two 3/3 red Shark enchantment creature tokens.

Whenever a card is put into a graveyard this turn, you may put it on the bottom of its owner's library.
Draw a card.

{T}: Add {C}. Spend this mana only to cast a creature spell with a creature type no creature you control has.

{T}: Add one mana of any color. If that mana is spent on a legendary creature spell, it enters with an additional +1/+1 counter on it.

Enchant creature
When Mystic's Mantle enters, draw a card.
Enchanted creature gets +1/+1.
Mirage {G} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

Reverberate {2}{G} (When you cast this spell, copy it if you paid its reverberate cost. The copy becomes a permanent when it resolves.)
Mystical Echo gets +1/+1 for each other Reflection you control.
Whenever you discard a card, Reflections you control gain trample until end of turn.

{T}: Mystical Elk becomes a copy of target creature card in your graveyard. Activate only as a sorcery. (It loses this ability.)

I, II — Look at the top four cards of your library. You may reveal a permanent card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.
Discovery — At the beginning of your end step, you may put a permanent card from your hand onto the battlefield.

When Naga Cultivator enters, you may put a land card from your hand onto the battlefield.

When Naiad of the Glen enters, create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)
Naiad of the Glen has trample as long as it has a +1/+1 counter on it.

When Naive Apprentice enters, each player creates a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)
As long as an opponent controls an artifact, Naive Apprentice gets +2/+0.

Choose one —
• Untap target creature. It gets +3/+3 until end of turn.
• Destroy target artifact or enchantment.