What about a Durant with a locked hidden ability?
No. Why would you even unlock Durant's ability lol
Also, can I use moves in different ways than normal (i.e. using Circle Throw to throw an opponent into something or using Flamethrower to burn down a part of the arena)?
That would be considered a roleplay action, and is up to the discretion of the ref.
Can Struggle Crit? It says nothing about it being unable to in the handbook, NDA, or DAT, but S0L1D G0LD thinks it does and I want to get a ruling on it before moving on.
The battle.
It should be able to, since nothing anywhere says Struggle doesn't crit.