The Mega Evolution ruling can be found in the Omnibus Thread. It was supposed to be included in the handbook, but a failure to communicate resulted in it not being included. It is not explicitly in the Omnibus Thread, but one can infer that the implication is that you must include Mega Evolutions in your action string and failure to include it in subs will result in the Mega Evolution not occurring.
"As with sleep and freeze, the Pokemon's confusion counter is checked at the start of its turn and the Pokemon snaps out of confusion if its confusion counter is 0. If it is not 0, however, then there is a 50% chance that the Pokemon will not perform its intended action, but will instead hit itself in confusion."
Dynamic Punch would not have inflicted confusion, because of this.