msem-instigator

Whenever Thundering Towershell attacks, return a creature card with mana value 5 or less from a graveyard to the battlefield under your control. Trigger a death knell of that creature.

Take an extra turn after this one. Exile Time in a Bottle.
Augmented — If you've spent {W}{U}{B}{R}{G} to cast spells this turn, draw three cards.

Destroy target non-Xirix permanent. If that permanent had mana value 6 or greater, take an extra turn after this one.

First strike
If one or more creature tokens would be created under your control, for each of those tokens, you may create three 2/2 green Cat Warrior creature tokens instead.

When Tinker Tantrum enters the battlefield and at the beginning of your upkeep, you may sacrifice an artifact. If you do, reveal cards from the top of your library until you reveal an artifact card with mana value X or less, where X is 1 plus the sacrificed artifact's mana value. Put that card onto the battlefield and the rest on the bottom of your library in a random order.

You may put cards with mana value 2 or less that permanents you control explore into your hand as though they were lands. (You won't get the counter if you do.)
Whenever Torch of Those Underfoot attacks, it explores. (Reveal the top card of your library. Put it into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then you may put that card in your graveyard.)

Whenever Tortle Veteran or another Turtle enters the battlefield under your control, that creature explores. (Reveal the top card of your library. Put it into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then you may put that card in your graveyard.)

Land creatures you control get +1/+1 and have vigilance.
Enchantment creatures you control get +1/+1 and have lifelink.
Artifact creatures you control get +1/+1 and have flying.

Creatures you control have “When this creature becomes tapped for the first time during each of your turns, untap it.”
{T}: Add one mana of any color.

As Tree of Timelines enters the battlefield, you may pay 3 life. If you don't, it enters the battlefield tapped.
{T}: Add {B}, {G}, or {U}.

Erratic, erratic, erratic (When this creature dies, reveal the top four cards of your library. Put a creature card that costs less than this revealed this way onto the battlefield and the rest on the bottom of your library in any order. Repeat this process twice.)

Copy target spell twice. You may choose new targets for the copies. (A copy of a permanent spell enters the battlefield as a token.)

At the beginning of your end step, draw a card if a creature died this turn. Then Tumultipede deals 2 damage to each opponent if two or more creatures died this turn. Then create three 1/1 green Saproling creature tokens if three or more creatures died this turn.

Whenever a creature enters the battlefield under your control, if it wasn't cast, you gain life equal to that creature's toughness and may draw a card.
[+2]: Return up to one target creature card from your graveyard to the battlefield.
[–3]: Create an 8/8 blue Kraken creature token.
[–9]: Each player exiles all creature cards from their graveyard, then sacrifices each creature they control. Put each creature card exiled this way onto the battlefield under your control.

If you would gain life, you gain twice that much life instead.
If you would draw a card, draw two cards instead.
If you tap a permanent for mana, it produces twice as much of that mana instead.

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
Other creatures you control have base power and toughness equal to this creature's base power and toughness.

{1}, Sacrifice another creature: Crystallize. Activate only as a sorcery. (Put a +1/+1 counter on a creature you control or create a Treasure.)
{W}{U}{B}{R}{G}: Target creature gets +3/+3 and gains trample until end of turn. Activate only as a sorcery.

You may play cards exiled with Azamir planeswalkers.
[+1]: Target player exiles a card from their hand.
[–3]: Exile target nonland permanent unless its controller exiles two other permanents they control.
[–7]: Target opponent may have you take two extra turns after this one. If they don't, you control them during their next turn.

{T}: Add {C}.
{3}{B}: Until end of turn, Tzhai's Throne becomes a 2/2 creature. It's still a land. It gets +2/+2 if {R} was spent to activate this ability, gets +2/+2 if {G} was spent, and gets +2/+2 if {W} was spent.

Concord — As long as there are four or more card types among permanents you control, you may cast the first spell you cast each turn without paying its mana cost.

Archive 0 (As this enters the battlefield, shuffle the top zero cards of your main library into a new face up library. Sacrifice this after the archived library is empty.)
As Undue's Study enters the battlefield, shuffle your graveyard into the archived library.

[+2]: Exile up to three target cards from graveyards.
[+1]: Create a 2/1 black Horse Zombie creature token with lifelink.
[0]: If Undue has six or more loyalty counters on him, each opponent returns a creature card of their choice from a graveyard to the battlefield under your control.

Mill four cards, then return any number of creature cards with total mana value 4 or less from your graveyard to the battlefield.

Enchant creature
As long as it's your turn, enchanted creature has indestructible.
Whenever enchanted creature attacks, it deals damage equal to its toughness to any target.

Lifelink
Augmented — Whenever you cast a spell, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, put a +1/+1 counter on United Guardian. It loses this ability and gains “Whenever United Guardian attacks, create two 1/1 blue Elemental creature tokens with flying that are tapped and attacking.”