Sacrifice stuck

So im at the second mission, i entered the deathgod portal twice.

And now i have killed every creature on this level + converted all into mana shrines... But now the main altar of the enemy won't go down... I press attack all the time, and I tried everything...

But the enemy wizard keeps coming back and the gate at the end of the level keeps closed because they say I have to destroy him...

I haven't played this game for a long time so i don't remember what im doing wrong :S

Could someone help me out on this? Is there something special u need to do at the altar?