Nature's beauty is all you need ,.. plus the Swordspider-form is very nice against mages and smaller opponents. His attacks are poisonous and *fast*.
Also, use the firesalamander-form to spit fire at your opponent .. aside from the spitting that form is useless though. I'd say the fire spitting and the Spider form are the only forms truly helpfull.
And yes, th gap from lvl 14 to 15 is huge
Fire-elementals ( lvl 6 spell ) are incredible btw