I usually love playing regulus as erebus. 
I use the cloak of the night too so I get an extra tp that doesn't take mana (one issue erebus has is sometimes if you don't gauge mana correctly after the bat swarm you don't have enough for the bite... often since regulus is back by towers this is dangerous because you are often reliant on the bite for enough health to follow through... doubly a problem if you just set off mines)
Anyway, yeah you need to health stack. bat swarm + bite will take you well passed half health if you don't. And mines at your feet is always good. Mines are also good for killing all his minions.
So yeah, let him have the flag.... mine your feet back by the tower... peck him till he gets annoyed... on bat swarm+bite let the mines + tower screw him over...
Oh, and don't bother much with the eye of betrayer. You're vulnerable when casting it, he can mist it off anyway, and it'll usually kick in during TP+bite when the slowdown part doesn't matter since he's on the offensive and right next to you and you're slow from the bite too anyway and the damage doesn't matter because he just recovered it from the bite.