Cataract?
UB + Blood of the Fallen + Banded = 2750 HP, IIRC., at level 1. Health flag on Cataract will push that beyond 3k baarely, and at level 1. Level up a bit and your health goes up, aand you've also got gold. Let's assume Hauberk and Unbreakable. I've had those by level 5 before while playing UB, admittedly I did get a kill, but a tower is still 300 GP. That's another 675 (Hauberk. Not available to look in game atm) and 600 from Unbreakable. That should seal the deal, I think.
HP stacking is very easy. I didn't even touch if he has a Sigil of Vitality.