MAKING A JUMP COMMAND.

Make a battle animation of the character jumping into the sky and inflict your character with a condition called "JUMPING" and set a switch called JUMPED to ON. Make that graphic for the condition blank so that your character appears to still be in the air (you might want to also make him resistant to all physical attacks, check that box as well). Then make a battle event that occurs after a couple turns that requires the switch JUMPED to be ON, and then call a battle animation to bring the hero jumping down onto the enemy and dealing damage.

This assumes you already know how to do these things in RM2k3. Let me know if you want me to break any of these steps down.

Does evade all attacks extend to skills?

Ah, that's true GRS. I suppose you could just set it to remove the party member for a set number of turns, then add him back in and deal damage to the enemy. But make sure that you make a parallel process common event that activates on the JUMPED switch to add the character back in if the battle finishes while he's midair.

The downside of this approach is that you will lose the battle if the rest of your party dies while the character is jumping.

EDIT: If you subbed the jumping character for a different temporary one with no battle graphic and 100% resistance to all types of damage, all hits (skills or otherwise) would deal 0 to the jumping character. But you'd have to work out the kinks of switching those characters in and out. This is probably the more viable approach.

Test it.