Here is my attempt!
Well done!

Sweet. Silent/Taciturn. Merciless (or ruthless) ->
Mila. Molchaliva. Besposhchadna/Bezzhalostna.
Milaya. Molchalivaya. Besposhchadnaya/Bezzhalostnaya *

*There are two forms of adjectives in Russian - short form and full form, the choice between them is a matter of style and manner of speech.