ok i have a spell that shoots and everything... but you can attack yourself.... and also it won't blow blow up when it hits something with density.... I tried to fix it but failed. this is what i have

mob/verb/fireball(mob/M)
src.mp -= 5
world << sound("spell.wav")
var/O = get_step(src,src.dir)
var/obj/S = new/obj/fireball(O)
walk(S,src.dir,0)
M.HP -= rand(15,20)
M.DeathCheck(src)
mob/Bump(atom/movable/A)
if(isobj(A) && istype(A, /obj/fireball))
flick("boomie",A)
del(A)

thanks, Aleis