Originally Posted by Typhox
The Damage is Pure damage. Pure damage gets blocked by BKB. But OD can still do a lot of auto attack damage (since he is int main) against the magic immune hero. BKB doesn't make you invincible against OD. It just reduces the damage youre taking. Also quite funny, the Pure damage works against heroes that are under Omni's ultimate.
Not exactly. BKB doesn't actually block pure damage. The reason why Arcane Orb gets blocked is because its damage AMOUNT is calculated as pure (not blocked by armour or magic reduction), but its damage TYPE is magic, which is blocked by magic immunity. This is a key difference, because it means that Hood of Defiance as well as AM's Spell Shield do not reduce the damage of Arcane Orb, but BKB, Repel, and Naix's Rage will block Arcane Orb's damage completely. The pure damage also means that armour will not reduce the damage of Arcane Orb, which is why Omni's ultimate, which grants +1000 armour, will not work against it.