Whenever one or more tokens your opponents control enter, for each of them, create a tapped token that's a copy of it. This ability triggers only once each turn.
Whenever one or more tokens you control enter, each opponent loses 1 life and you gain 1 life.

Pack Rat's power and toughness are each equal to the number of Rats you control.
, Discard a card: Create a token that's a copy of this creature.

First strike, trample
When this creature enters, you may search your library for up to two artifact, creature, and/or enchantment cards with mana value 1 or less, reveal them, put them into your hand, then shuffle.

When Spider-Man 2099 enters, return up to one target creature to its owner's hand.
Whenever one or more creatures you control deal combat damage to a player, draw a card.

Dark Depths enters with ten ice counters on it.
: Remove an ice counter from Dark Depths.
When Dark Depths has no ice counters on it, sacrifice it. If you do, create Marit Lage, a legendary 20/20 black Avatar creature token with flying and indestructible.

Equipped creature gets +1/+1.
Whenever equipped creature attacks, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
Equip

Whenever a creature attacks, you gain 1 life.

Creatures you control get +1/+1.
Whenever a creature you control enters, this enchantment deals 1 damage to each opponent.

This creature gets +1/+1 for each other creature on the battlefield named Relentless Rats.
A deck can have any number of cards named Relentless Rats.

This creature enters with X +1/+1 counters on it.
: Put a +1/+1 counter on this creature.
Remove a +1/+1 counter from this creature: It deals 1 damage to any target.

Ward (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays .)
If one or more tokens would be created under your control, twice that many of those tokens are created instead.

Flying, protection from white and from black
When Ureni enters, it deals X damage divided as you choose among any number of target creatures and/or planeswalkers your opponents control, where X is the number of lands you control.

Put a flood counter on target land. That land is an Island in addition to its other types for as long as it has a flood counter on it. If you control a Merfolk, draw a card.

Whenever you cast a creature spell, you may draw a card.

Menace
Whenever Black Widow deals combat damage to a player, that player exiles cards from the top of their library until they exile a nonland card. You may put a +1/+1 counter on Black Widow. If you don't, you may cast the exiled nonland card until end of turn and mana of any type can be spent to cast that spell.

Creatures with power 3 or greater don't untap during their controllers' untap steps.

Flying, first strike, lifelink, protection from Demons and from Dragons

When this enchantment enters, you draw four cards and you lose 4 life.
At the beginning of your upkeep, if you control four or more Demons with different names, you win the game.

(: Add or .)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Station (Tap another creature you control: Put charge counters equal to its power on this Spacecraft. Station only as a sorcery. It's an artifact creature at 20+.)
10+ | Whenever you attack, Dawnsire deals 100 damage to up to one target creature or planeswalker.
20+ | Flying