Since it's a technique, that might be just a renamed Spell command, and not Spell subset. With that, you could set a spell to a switch spell, then once that switch is on, make a page in the monster group. For Arche's meteor type spell, that would mean you play a battle animation on an enemy, remove a certain amount of health from them, and continue it for every enemy you have there. I would make a type of formula for the damage done, you could look up the battle algorithms in the RM2k3 help file, if you want to do it that way, then just randomize it a little bit.
Or if you have spell subsets instead of a spell command, It's possible that they set the characters MP to a variable. Since every spell has a different cost, then they check the characters MP using a new variable after they use the spell command. If the characters MP (variable 2) is 38 less than the original characters MP (variable 1), then that means they used x spell, let's say Fire2. Then set on the switch for Fire2 and make a page in the monster group for that. Then it's the same as the first step.
If you want a regular attack to hit twice, then you could simply set your weapon to attack twice. Or in the Item tab, go to your weapon, click "Set" under the character animation, then you'll see a "number of attacks" in the new screen.