This is a simply ruling question I feel like asking, one that is easy and most should know it.

Ally of Justice, Catastor.

Atk/ 2200 Def/ 1200

At the start of the Damage Step, if this card battles a non-DARK monster: Destroy that monster.


Neo-Spacian Grand Mole

Atk/ 900 Def/ 300

At the start of the Damage Step, if this card battles an Opponent's monster: You can return both monsters to the hand. ( Without damage calculation. )


Player A has Ally of Justice, Catastor.
Player B has Neo-Spacian Grand Mole.

Player A enters his battle phase and declares an attack with Ally of Justice, Catastor to an his/her opponent's Neo-Spacian Grand Mole.
Who's effect triggers first, sending/destroying the other?

I know the answer 

Turn Player gets to say what effect goes off first.

That is true, True Skills, but Grand Mole's effect is the one that triggers, sending the other to the deck. Catastor attacks into Grand Mole, Catastor triggers, then Grand Mole can chain to Catastor, since Catastor is mandatory and Grand Mole is optional. So, Grand Mole sends Catastor to the extra deck and Catastor's effect fizzles.

catastor resolve wiithout eff

i think Grand mole would work and castor would go back to the extra deck

Both are returned, beacuse catastor's effect activates first.