I was able to use a completely different approach that
didn't use invuln pots to get through hell. To beat it, I needed:
- health potions
- one teleport scroll
- 6 imp invocation scrolls
- fire scroll
First, you have to get through the first wave of demons. As you work your way through the demons, fight through a spiked wall that spawns ghosts in the next wave (top two or bottom two lanes).
As often as you have an available cooldown from here out, take a health pot. They're so cheap, anyway.
Once teleported back by the
*, send out an imp on each available scroll cooldown. You may only get 3 out before you bump into the imps at the front. Teleport back, send out two more imps to make a conga line, as shown in the picture.
(Side note, the teleport and more imps are not required, depending on how successfully you got through the first wave of demons and how many more cooldowns of HP pots you need)
The reason for this line is as the imps slowly get through the second wall and the second teleporter, you have more time to pop pots, ensuring you're at full health. As the imps break through, you're teleported to the start of the lane, send out one imp (or more!) and take on devil and slaughter him with the fire scroll.
Note: I realize 680 HP might be more than many are taking on the devil with, but this was one way to defeat the Devil without invuln pots.