Are the underlined natural phrases? Any suggestions please about these sentences?

The river was at its most spectacular.

Our lion was at his most ferocious.

His attitude was almost always negative, but that night it was at its worst.

Shoba was at her ugliest that night, shouting and screaming like a complete psycho.



Mr. TomAre the underlined natural phrases?

Yes, but you probably won't hear this construction very often, particularly those like the first two, which are very literal. In my opinion it's more successful when used for things like attitude and behavior (your second two examples).