One of most hilarious ways to make Mages hate you is to pick Huge (or whatever it's called) Merit and use some subtle means (including magic) to look like old plain Size 5 Person. Potency 1000000000000000000000 single target nuke? Not working if your Size Factor is 1!
Though seriously using shape changing magic to escape spells is legit tactic. And it's actually a mythological trope where magican duels often involved complicated game of "I turn into X which you counter by turning into Z which makes me turn into K which you counter by turning into..."