Cheapest priced copy (Throne of Eldraine): $0.35 at Card Kingdom, near mint, their price list as of .
Outmuscle 
Sorcery · Common · Throne of Eldraine · #170
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.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Throne of Eldraine | 170 | Common | $0.35 | $0.49 |
| The List | ELD-170 | Common | $0.35 | — |
8 rulings from Wizards of the Coast
- 4 October 2019If 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.
- 4 October 2019Adamant 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.
- 4 October 2019If 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.
- 4 October 2019You can't cast Outmuscle unless you choose both a creature you control and a creature you don't control as targets.
- 4 October 2019Because 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.
- 4 October 2019If 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.
- 4 October 2019If either target is an illegal target as Outmuscle tries to resolve, neither creature will deal or be dealt damage.
- 4 October 2019If 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.