[Burnsaber]

Okay, I did some more testing. The thing worked like a charm, but the Polymorph effect is permament, the commander will not revert back after the battle. However, You can counteract this by giving the form they will transform into #firstshape. To make it a lot simpler, here is how the trick works:

You have commander A that you want to transform into unit B for battle. Create a custom #onebattlespell for unit A that transform it into unit B. Give unit B firstshape back to A, so that it will revert back into A after the battle. The dwarf mod is going to use this trick on two commanders to make them lose caster levels in combat.

Unfortunately it seems that the " Form of the Dragon" spell I advertised couple of posts ago is not possible though, since my trick is only going to work if you know what mage is going to cast the spell.

Anyways, below is the bare bones code for the spell. By casting the custom "Summon Earthpower", the caster is going to transform into a slinger (unit nmbr 50) and then transform into a battle vestal (unit nmbr 51) after the battle (because I edited the slinger unit to have battle vestal as first shape).

#selectmonster 50
#firstshape 51
#end

#newspell
#name "Testing"
#descr "..testing.."
#school 4
#researchlevel 0
#effect 54
#aoe 1
#explspr 10030
#damage 50
#path 0 3
#pathlevel 0 1
#fatiguecost 0
#spec 64
#end

#newspell
#copyspell "Summon Earthpower"
#nextspell "Testing"
#school 4
#researchlevel 0
#path 0 3
#pathlevel 0 1
#end