Battle — Siege // Sorcery
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, up to two target creatures each get +2/+0 and gain vigilance and haste until end of turn.
Sorcery
Create two 3/2 red and white Warrior creature tokens with "Whenever this token and at least one other creature token attack, put a +1/+1 counter on this token."
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.
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.