The EffectPolymorph() NWScript command creates an effect that will polymorph the creature it is applied to. This effect should be applied temporarily or permanently (not instantly).
Definition
effect EffectPolymorph (int nPolymorphSelection, int nLocked=FALSE)
int nPolymorphSelection- A POLYMORPH_TYPE_* constant indicating which form the effect will produce.
int nLocked- If FALSE (the default), players will be given a "cancel polymorph" option on their character's radial menu while this effect is applied.