Outmuscle — ruling 1

You can't cast Outmuscle unless you choose both a creature you control and a creature you don't control as targets.

Outmuscle — ruling 2

If either target is an illegal target as Outmuscle tries to resolve, neither creature will deal or be dealt damage.

Outmuscle — ruling 3

If the creature you control is an illegal target as Outmuscle tries to resolve, no creature gets a +1/+1 counter. If that creature is a legal target but the creature you don't control isn't, it still gets a +1/+1 counter and gains indestructible if appropriate.

Outmuscle — ruling 4

Because state-based actions don't destroy a creature with lethal damage marked on it until a player would receive priority, gaining indestructible from Outmuscle will save your creature if it's dealt lethal damage in the fight.

Outmuscle — ruling 5

If an instant or sorcery spell has an adamant ability, you perform the spell's instructions in order. You don't perform the adamant instruction before the spell resolves or before any other effects printed above it.

Outmuscle — ruling 6

If an effect allows you to cast a spell without paying its mana cost, you can't choose to cast it and pay unless another rule or effect allows you to cast that spell for a cost. Similarly, you can't waive a cost reduction unless that effect says you may.

Outmuscle — ruling 7

Adamant effects check what mana was actually spent to cast a spell. If an effect allows you to spend mana “as though it were mana” of any color or type, that allows you to spend mana you couldn't otherwise spend, but it doesn't change what mana you spent to cast the spell.

Outmuscle — ruling 8

If you copy a spell that has an adamant ability, no mana was spent to cast the copy at all, so that ability won't apply.

Outmuscle : règles, fonctionnement et interactions (MTG)

Outmuscle is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Put a +1/+1 counter on target creature you control, then it fights target creature you don't control. (Each deals damage equal to its power to the other.) Adamant — If at least three green mana was spent to cast this spell, the creature you control gains indestructible until end of turn.

How it works : Outmuscle

Original English text — Wizards of the Coast / Scryfall

#1October 4, 2019· Wizards of the Coast
You can't cast Outmuscle unless you choose both a creature you control and a creature you don't control as targets.
No other card is named in this ruling.
#2October 4, 2019· Wizards of the Coast
If either target is an illegal target as Outmuscle tries to resolve, neither creature will deal or be dealt damage.
No other card is named in this ruling.
#3October 4, 2019· Wizards of the Coast
If the creature you control is an illegal target as Outmuscle tries to resolve, no creature gets a +1/+1 counter. If that creature is a legal target but the creature you don't control isn't, it still gets a +1/+1 counter and gains indestructible if appropriate.
No other card is named in this ruling.
#4October 4, 2019· Wizards of the Coast
Because state-based actions don't destroy a creature with lethal damage marked on it until a player would receive priority, gaining indestructible from Outmuscle will save your creature if it's dealt lethal damage in the fight.
No other card is named in this ruling.
#5October 4, 2019· Wizards of the Coast
If an instant or sorcery spell has an adamant ability, you perform the spell's instructions in order. You don't perform the adamant instruction before the spell resolves or before any other effects printed above it.
No other card is named in this ruling.
#6October 4, 2019· Wizards of the Coast
If an effect allows you to cast a spell without paying its mana cost, you can't choose to cast it and pay unless another rule or effect allows you to cast that spell for a cost. Similarly, you can't waive a cost reduction unless that effect says you may.
No other card is named in this ruling.
#7October 4, 2019· Wizards of the Coast
Adamant effects check what mana was actually spent to cast a spell. If an effect allows you to spend mana “as though it were mana” of any color or type, that allows you to spend mana you couldn't otherwise spend, but it doesn't change what mana you spent to cast the spell.
No other card is named in this ruling.
#8October 4, 2019· Wizards of the Coast
If you copy a spell that has an adamant ability, no mana was spent to cast the copy at all, so that ability won't apply.
No other card is named in this ruling.