Garbage Elemental

Last strike (This creature deals combat damage after creatures without last strike.)
Battalion — Whenever Garbage Elemental and at least two other creatures attack, target creature can't block this turn.

Unstable

Frenzy 2 (Whenever this creature attacks and isn't blocked, it gets +2/+0 until end of turn.)
Garbage Elemental can't be blocked by wordy creatures. (A creature is wordy if it has four or more lines of rules text.)

When Garbage Elemental enters the battlefield, it assembles a Contraption. (Put the top card of your Contraption deck face up onto one of your sprockets.)
Undying (When this creature 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.)

When Garbage Elemental enters, it assembles a Contraption. (Put the top card of your Contraption deck face up onto one of your sprockets.)
Undying (When this creature 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.)

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)
When Garbage Elemental enters the battlefield, roll two six-sided dice. Create a number of 1/1 red Goblin creature tokens equal to the difference between those results.

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)
When Garbage Elemental enters, roll two six-sided dice. Create a number of 1/1 red Goblin creature tokens equal to the difference between those results.

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom of your library in a random order.)
When Garbage Elemental enters the battlefield, roll a six-sided die. Garbage Elemental deals damage equal to the result to target opponent.

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
When Garbage Elemental enters, roll a six-sided die. Garbage Elemental deals damage equal to the result to target opponent or planeswalker.

Unleash (You may have this creature enter the battlefield with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.)
Each creature you control with any kind of counter on it has art menace. (They can't be blocked except by creatures with two or more visible figures in their art.)

Unleash (You may have this creature enter with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.)
Each creature you control with any kind of counter on it has art menace. (They can't be blocked except by creatures with two or more visible figures in their art.)

If you give first strike to a creature with last strike, it’ll deal combat damage twice: once during first-strike combat damage and again during last-strike combat damage. If you give a creature double strike to a creature with last strike, it’ll deal combat damage three times: once during first-strike combat damage, again during normal combat damage, and again during last-strike damage. Essentially, double strike + last strike = triple strike.

Last strike is opposite of first strike. A creature with last strike deals combat damage after when most creatures deal combat damage. A creature with last strike deals combat damage only if it survives both first-strike and normal combat damage.