Battle — Siege // Artifact Creature — Construct
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, exile target nonland permanent an opponent controls that isn't exactly two colors.
Artifact Creature — Construct
Whenever you cast a spell that's exactly two colors, look at the top six cards of your library. You may reveal a card that's exactly two colors from among them and put it into your hand. Put the rest on the bottom of your library in a random order.
This triggers when the spell is cast, before it resolves. Even if the spell is countered, the cast trigger still resolves. Copies of spells are not cast, so they won't trigger this.
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.