Battle — Siege // Creature — Zombie
Battle — Siege
(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When this Siege enters, each player mills three cards, then each opponent discards a card and you draw a card. (To mill three cards, a player puts the top three cards of their library into their graveyard.)
Creature — Zombie
You may have this creature enter as a copy of any creature card in a graveyard, except it's a 4/4 black Zombie in addition to its other colors and types.
This card uses a replacement effect ('as [it] enters' or 'enters with') to modify how the permanent enters. This is NOT a triggered ability — it can't be responded to, and effects like Panharmonicon or Torpor Orb don't affect it.
Copies don't copy counters, equipment, auras, or other external modifications. A copy of a transformed card copies only the front face. If the copy enters the battlefield, it triggers its own ETB abilities.
This card's ability triggers when it enters the battlefield, not when it's cast. Effects that double ETB triggers (like Panharmonicon) work here. Countering the spell prevents the creature from entering, so the ETB won't fire.