Beidou's Q snapshot timing
Youtube: No snapshot, Skill DMG 16444, Lightning DMG 8906 (The difference of the Skill DMG is due to losing 1 stack of Serpent Spine.)
Does Beidou's burst snapshot?
Beidou's burst (can snapshot) still persists even when the current character (except Beidou) dies. For example, XQ's rain swords / Eula's Lightfall Sword animation do depend on the character's attack, hence, do not have snapshot mechanics.
Does Eula ULT snapshot?
Eula's LightFall Sword does not have snapshot mechanics and is calculated in real time.