Does Abandoned Hall trigger when you cast a spell or when the spell finishes resolving?

Ruling: Abandoned Hall triggers when a spell finishes resolving. The phrase "when you play a spell" means after the spell has completed its resolution process, not when it is initially cast.

Sequence:

• You play a spell and it resolves (executes its effects)
• After the spell finishes resolving, the "when you play a spell" condition is met
• Abandoned Hall's triggered ability is placed on the chain

Nuances:

• If a spell is countered (defied), it never finishes resolving and is not considered to have been "played," so Abandoned Hall will not trigger.
• Even if a spell's instructions fail (e.g., due to mistargeting), it still counts as having been played because it completed the resolution process.