We will go to the game even if it rains. Here 'even if it rains' is?

Noun phrase

Adjective phrase

Adverb clause

None of these

"Even if it rains" is an adverbial clause because it modifies the verb "will go".

It indicating the condition under which the action (going to the game) will happen.

It explains when or under what condition the action will take place, which is characteristic of an adverb clause.