Unaware of Lorwyn's diversity, it sees only itself, reflected a thousand times over.

Mirror Entity

Changeling (This card is every creature type.)
{X}: Until end of turn, creatures you control have base power and toughness X/X and gain all creature types.

Outlaws of Thunder Junction Commander

Murders at Karlov Manor Commander

The List

Commander Legends: Battle for Baldur's Gate

Crimson Vow Commander

Activating the ability with X = 0 will cause all creatures you control to become 0/0 and be put into the graveyard.

Changeling applies in all zones, not just the battlefield.

Mirror Entity's ability overwrites any effects that previously set a creature's base power and/or toughness. Any existing effects or counters that raise or lower a creature's power and/or toughness continue to apply to the creature's newly-set power and toughness.