msem-instigator

When Ageless Weaver enters, create a green Aura enchantment token named Years of Experience attached to target creature. The token has enchant creature and “Enchanted creature gets +2/+2.”
Whenever an enchanted creature you control dies, create a 3/3 green Elemental creature token.

Flying, haste
Thermal Surger can't block.
When Thermal Surger enters, you may sacrifice a land or exile a land card from your graveyard. If you do, put a +1/+1 counter on Thermal Surger.

Haste, prowess
Wanderlust — When Spitfireling enters, if you control four or more differently named lands, create two 1/1 red Elemental creature tokens with prowess and haste.

Discard a land card: Draw a card. Shardstorm Elemental gets +1/+0 and gains flying until end of turn. Activate only once each turn.

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.

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.”

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.

When Pyroclastic Maw enters, destroy target land. If that land was nonbasic, Pyroclastic Maw gains haste until end of turn.

Whenever a nonbasic nontoken land enters under an opponent's control, create a tapped colorless land token named Fading Rift with “{T}, Sacrifice this land: Add one mana of any color.”

When Journey to the Otherworlds enters, draw a card, then choose a creature card name.
Whenever a creature you control with the chosen name attacks, you may aetherize it. (To aetherize, create a token that's a copy of it, then exile that token.)

Whenever a creature enters, it deals damage equal to its power to any target of its controller's choice.
When Interplanar Raid enters, you may aetherize target creature you control. (To aetherize, create a token that's a copy of it, then exile that token.)

When Incense Stoker enters, you may return target instant or sorcery card with mana value less than or equal to the number of differently named lands you control from your graveyard to your hand.

Whenever an opponent casts a spell during your turn, Hunter of Incantations deals 2 damage to that player.

Target creature you control gets +2/+0 until end of turn. If that creature is attacking, you may aetherize it. (To aetherize, create a token that's a copy of it, then exile that token.)

Gain control of target creature until end of turn. Untap that creature. Until end of turn, it gains haste and “Whenever this creature deals combat damage to a player, aetherize it.” (To aetherize, create a token that's a copy of it, then exile that token.)

Crater Burst deals 3 damage to any target. Add {W}{U}{B}{R}{G}. Until end of turn, you don't lose this mana as steps and phases end.

Wanderlust — When Ardent Explorers enters, if you control four or more differently named lands, create a 1/1 Scout creature token that's all colors. That token gains haste until end of turn.

First strike, menace
When Zhargetan Reclaimer enters, put any number of cards your opponents own from exile into their owners' graveyards. If three or more cards were put into graveyards this way, create two 1/1 Scout creature tokens that are all colors.

{T}, Pay 1 life: Add one mana of any color that a land an opponent controls could produce.

Flash
If an opponent would draw a card, that player exiles the top card of their library instead. During each player's turn, that player may play that card for as long as it remains exiled.

If a creature card would be put into an opponent's graveyard from anywhere, instead exile it, then copy it. You may cast the copy. (You still pay its costs, including color. Copies of permanents enter as tokens.)

At the beginning of your upkeep, each opponent mills two cards.
{3}{B}: Exile target nonland card from an opponent's graveyard. Copy it. You may cast the copy. Activate only as a sorcery. (You still pay its costs, including color. Copies of permanents enter as tokens.)

As long as Shambling Morass is on the battlefield or in your graveyard, it's a land in addition to its other types.
When Shambling Morass dies, you may pay {1}. If you do, you draw a card and you lose 1 life.

Lifelink
When Seeker of Lost Secrets leaves the battlefield, you may pay 2 life. If you do, search your library for a card, put that card into your hand, then shuffle.

When Razorshell Marauder enters, you may sacrifice a land or exile a land card from your graveyard. When you do, target creature gets -1/-1 until end of turn and can't block this turn.