My opponent controls Raph & Mikey, Troublemakers. They tap Raph & Mikey to declare attackers. In response to the triggered ability of Raph & Mikey, Troublemakers (Whenever Raph & Mikey attack...), I cast Containment Priest from my hand using Flash.

When Raph & Mikey’s triggered ability resolves, the top of their library is revealed until a creature card is found: Summon: Bahamut is revealed.

Per rules interaction:

• Containment Priest’s static ability applies: If a nontoken creature would enter the battlefield and it wasn’t cast, exile it instead.
• Summon: Bahamut should be exiled directly without entering the battlefield at all.

Incorrect Behavior Observed

Summon: Bahamut was exiled as intended, but its Saga Chapter I ability triggered while in the exile zone—this should not happen, because Saga chapter abilities only trigger when the Saga enters the battlefield (not from exile).

Expected Correct Behavior

1. Summon: Bahamut is exiled by Containment Priest’s replacement effect and never enters the battlefield.
2. No Saga chapter abilities of Summon: Bahamut trigger at any point, especially not in exile.