My name is Ozymandias, King of Kings:
Look upon my works, ye Mighty, and despair! Nothing beside remains. Round the decay Of that colossal wreck, boundless and bare The lone and level sands stretch far away.
The moment in writing where a character, usually the main character, loses everything or realizes they've lost everything, especially after they have gained more than what they originally had in terms of financial and material wealth, power and notoriety, fame, etc. Named after the sonnet of the same name, in which the once great Ozymandias has been reduced to a crumbled statue.
Ace's Ozymandias Moment was very impactful in showing that he bit off more than he could chew, and paid the price.