The moment his interests were harmed, he immediately showed his vicious side.
Tips
usage
毕 here means 'fully / completely' (as in 毕业 'finish studies', 毕生 'whole life'). The image: a previously hidden ferocious face now totally on display. Strongly negative, used when someone drops a polite mask and reveals genuine cruelty.
register
Common in news writing, fiction, and dramatic spoken Chinese. Compare with 原形毕露 (yuánxíng bìlù, 'true form fully revealed'), which is broader, any hidden nature exposed; 凶相毕露 specifically frames it as ferocious/menacing.
