i was just playing with shapeshift today, and no you cant use fire breath or anything like that
but on the plus side, you get massive hp when you transform! the iron golem wins the award for highest hp with 465, and the balor comes in second with 451. the red dragon has around 350 something...and the fire giant and death slaad are around 300ish if i remember correctly
all you can do in your altered form is attack