Tā de zhànshù biànhuàduōduān, duìshǒu zhuōmō bùtòu.
His tactics shift in countless ways — opponents can't pin him down.
Tips
history
Attested in Feng Menglong's Ming collection 《古今小说·陈从善梅岭失浑家》: describing the Monkey King — '齐天大圣神通广大，变化多端.' Evocative of magical shape-shifting, which is still where the idiom shines.
usage
Neutral to slightly admiring for tactics/strategy/weather; slightly wary for market/situation. Not for describing a person's moods — for that use 喜怒无常.
