Whenever you attack, each opponent loses X life and you gain X life, where X is the number of attacking creatures. If Mishra, Claimed by Gix and a creature named Phyrexian Dragon Engine are attacking, and you both own and control them, exile them, then meld them into Mishra, Lost to Phyrexia. It enters the battlefield tapped 9/9 and attacking.
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Meld Partner: Phyrexian Dragon Engine
When Melded, it becomes the following:
Mishra, Lost to Phyrexia
Legendary Artifact Creature — Phyrexian Artificer
Whenever Mishra, Lost to Phyrexia enters the battlefield or attacks, choose three —
• Target opponent discards two cards.
• Mishra deals 3 damage to any target.
• Destroy target artifact or planeswalker.
• Creatures you control gain menace and trample until end of turn.
• Creatures you don't control get -1/-1 until end of turn.
• Create two tapped Powerstone tokens.

NOTE: Stock image, not actual card.