変 change

The egg changes into a HEN after hatching.

Each red Communist changes into a yuppie when they turn 30.

transformation, change ★★★★★
変 (change) + 化 (transform) = 変化 (transformation, change)

that's terrible! ★★★★★
大 (big) + 変 (change) = 大変 (that's terrible!)

this has 2 meanings, both used equally often:

"Tony is tai hen!" , for instance, could mean:

a) I feel sorry for Tony because his job sucks and his girl is cheating.

b) Tony is a really scary, mean person.　

perv ★★★★☆
変 (change) + 態 (looks like) = 変態 (perv)

What your brother and sister call you when they catch you peeking in the bathroom while they're doing it in the toilet.