If you go and look in the tutorials section there are a couple that deal with shape shifting/replacing an actor with another temporarily. The easiest way to do this would be to just change the character to a seperate actor with the monsters stats/skills and use a variable to store the players level and change the monster actors level accordingly.
You'd also need to have an event in the troops database tha activates via switch (turned on when skill is used) that adds 1 to a variable at the end of each turn and reverts the transformed actor to normal when the count reaches 10, resets variable to 0 and turns tube switch off. This Can be achieved by copy/pasting into every troop or usin yanfly's common troop event script to only have to set it up once. Last make a common event that activates by the same switch the troop event does and reverts the character back to normal; unless you want them to remain transformed after battle.
