Collocations for formidable - adj.

be, look, seem
The task looks formidable.

remain
find sth
Men found her formidable.

make sth

extremely, fairly, very, etc.
a very formidable opponent

a little, slightly, etc.

Formidable is used with these nouns:
adversary, array, barrier, challenge, challenger, character, competitor, enemy, foe, force, intellect, obstacle, opponent, personality, presence, record, reputation, rival, talent, task, warrior