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As Chang'e, evade an enemy ability using Moonlit Waltz that would have hit you for 500 damage or more.

Chang'e's second ability is Moonlit Waltz; it functions like a shorter Sanctuary, rendering you unable to be hit and restoring mana for any hits you would have sustained. Going for a pure power build is recommended here, as it's easier for abilities to hit for 500 damage when you have no armor.

You'll want to bait your opponent, then dodge as the ability is incoming. How you go about this largely depends on enemy team composition, though some enemies telegraph this better than others. I found the best three to dodge were Kukulkan, Odin, and Scylla.

Kukulkan: Watch for Kukulkan to do a backflip while facing you and the audio cue for his ultimate.
Odin: Watch for his Raven Shield. On offense, Odin will use this just before jumping. You may want the Phantom relic in case he starts a cage match after landing.
Scyllla: She has two moves to watch. The first is a lobbed acid ball that creates a slow AoE that can be detonated. Be ready to dodge as soon as it lands. The second is her ultimate, which stops her, has a charge time, and shows the area she's going to hit.

This is hardly an exhaustive list of who to get the achievement from, but should be some of the more common ways to unlock the achievement, as well as give a decent idea of what you should be doing.