Useing magic to attack is a simple thing. You use whatever type of magic you can, and create spells. If you are a vampire, you should have vampiric powers. Such as stealing ones' energy. If you are a completely magical creature, made from energy, you need and use your magic to transform.
Unicorns have three forms.
There first is there normal, there secound is human, and third is whichever they choose to have. But if you are a WereWolf, you'd use the energy to change only into human form. Humans who have strong magic will it to come to them. Normally in there first days of useing magic it's spontaneious to them. Dragons can breath fire, mist, and ice.