When Contagion Clasp enters the battlefield, put a -1/-1 counter on target creature. {4}, {T}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

When Contagion Engine enters the battlefield, put a -1/-1 counter on each creature target player controls. {4}, {T}: Proliferate, then proliferate again. (Choose any number of permanents and/or players, then give each another counter of each kind already there. Then do it again.)

As Door of Destinies enters the battlefield, choose a creature type. Whenever you cast a spell of the chosen type, put a charge counter on Door of Destinies. Creatures you control of the chosen type get +1/+1 for each charge counter on Door of Destinies.

As Herald's Horn enters the battlefield, choose a creature type. Creature spells you cast of the chosen type cost {1} less to cast. At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.

Creatures you control are every creature type. The same is true for creature spells you control and creature cards you own that aren't on the battlefield. {3}, {T}: Create a 2/2 blue Shapeshifter creature token with changeling. (It is every creature type.)

Spells you cast have ripple 4. (Whenever you cast a spell, you may reveal the top four cards of your library. You may cast spells with the same name as that spell from among the revealed cards without paying their mana costs. Put the rest on the bottom of your library.)

As Adaptive Automaton enters the battlefield, choose a creature type. Adaptive Automaton is the chosen type in addition to its other types. Other creatures you control of the chosen type get +1/+1.

Whenever Ashcoat of the Shadow Swarm attacks or blocks, other Rats you control get +X/+X until end of turn, where X is the number of Rats you control. At the beginning of your end step, you may mill four cards. If you do, return up to two Rat creature cards from your graveyard to your hand. (To mill a card, put the top card of your library into your graveyard.)

All Rats have fear. {T}, Sacrifice a Rat: Create X 1/1 black Rat creature tokens, where X is the number of Rats you control.

As Metallic Mimic enters the battlefield, choose a creature type. Metallic Mimic is the chosen type in addition to its other types. Each other creature you control of the chosen type enters the battlefield with an additional +1/+1 counter on it.

Rat Colony gets +1/+0 for each other Rat you control. A deck can have any number of cards named Rat Colony.

Black creatures get +1/+1.

Enchant creature Enchanted creature gets +10/+10 and has trample and annihilator 2. (Whenever it attacks, defending player sacrifices two permanents.)

Commander creatures you own have "Whenever this creature becomes tapped, it and other creatures you control that share a creature type with it each get +2/+0 and gain undying until end of turn." (When a creature with undying dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)

{2}, {T}: Add {B} for each Swamp you control.

Search your library for a card, put that card into your hand, then shuffle.

Return target creature card and all other cards with the same name as that card from your graveyard to your hand.

Choose a creature type. Destroy all creatures that aren't of the chosen type.

Return up to two target creature cards from your graveyard to your hand, then discard a card.

You draw two cards and you lose 2 life.

Each player chooses a creature type. Each player returns all creature cards of a type chosen this way from their graveyard to the battlefield.

Scry 2, then draw two cards. You lose 2 life.