For every 2 turns, it deals a whopping 5 damage.
Immortal: Every 2 turns, it deals 8 damage.
Get the picture?
of course but your failing to see that cosmic worm would have more survivablity than the immortal against certain shields, for example, fire shield, the immortal would die in 3 turns = 12, but the cosmic worm would die in 6 = 15, and in the end do more damage but to nerf this, the cosmic worm is targetable by spells everytime it comes back so in another sense it has either more or equal survivability to immortal.
but you guys have made me think a little more on the matter and now i have reached a decision and im going to increase attack, so then it will pose a little more difference to the immortal.