One easy way to beat the goblin challenge is to spam Time Stop spells. Goblins will stop pouring in during that, and your army can just carve its way to the enemy base. You'll need to have mana at pretty much max (400) and remember to watch the timer, since it takes about three seconds for the spell to take effect, so you don't want any gaps. You'll also need to get rid of the black goblins with a meteor strike just before starting the assault.
 "Epic War 4"){kind=icon}