Here is my reply:
Assuming its the end of the other persons turn then no as I don't have any untapped mana. If it's my turn, what other spells do I have in hand? Do I have any reason not to wait to blow up null champion in response to his attempt at the third level next turn? If the question is do you kill champion (in resp to lvl 3) or adept then i'd need to know what sort of capacity I have to block champion and still win. Otherwise champion in response to his third lvl on his next turn I guess?