Hi sunray,
1d. [Opponent], slightly unusual synonym for crazy + Roman Emperor short of his final letter.
22a. [Decide], definition is to limit (unusual word), synonym for a number of horses in a Scottish word for yard.
35a. [Trade], a fast (religious) + risks last sing one of the alternatives for king.
18a as you've noted is "normal" ie no extra word.
There's an alternative to calf and is a homophone (call) of to aid.