Druid Help

I've made a spell based on bear form for Druid Of the Claw that transform the Druid into a bear.But if i add my custom spell to another unit,change tho options
of my spell so that it will transform my druid > polar bear (a new custom unit based on Bear Unit Form from druid of the claw) and in the game that spell doesn't work.What is the problem?Or what spell must i use to transform the
druid into an other creature??

i don't need more help....I've found what i was searching :D