Quote Originally Posted by ATHATH View Post
Why SHOULDN'T the Assassin get advantage (and thus Sneak Attack) on his attack roll? They're attacking from stealth after presumably using their bonus action to enter stealth.
You kind of missed the bit where the OP said they'd lower the Rogue's level, making them no longer an Assassin.

Attacking a creature in combat from Stealth doesn't give you advantage on the attack roll, unless the DM specifically allows it. (PHB 177)

Attacking a surprised creature doesn't give you advantage on the attack roll, unless you have an ability that specificaly allows it.