I'm going to do a full write-up on what is needed for this, for anyone else who needs this in the future.

You will need the Cloak of the Forest and Shield of the Mountain, both gained from recipe scrolls (the walkthrough does cover these at least), the Horn you get from the Inferno, and the Wizard's Virge.

To get the Virge, you need to give the Ratling at the entrance to Ratlington a red gem (ON THE FIRST VISIT!!!), to get an item to give to the trickster stand-in (the name escapes me, sorry), for the Scope. IF YOU MISS THIS, you can simply use the console to spawn in the Scope with the following code:

spawn("scope")

Once you have the Scope by whatever means, go to the top of the north-east tower in Goldhaven and use the Scope to teleport to the Homeworld, there you will be given the Wizard's Virge, place the Scope on the pedestal to warp back.

With the Virge, go to the Inferno and destroy the "shadow flame demons", be sure to bring a few recharges, the Virge only has one charge. When the correct demon is slain, the wall behind it will open, a short passage will open into a room with an altar, place the Amulet of Power on it to get the Horn.

Return to the Deeps and play the horn in the circle of stones to open the path, first altar place the Cloak and the path will open, continue to the second altar and place the Shield on it, the third altar needs the Horn, and finally the fourth needs the Wizard's Virge.

WARNING: past this point is the True Final Boss, the Ancient Evil, a mega buffed Viper Roots with loads of support from slimes, twigroots and those paralyzing bugs. The spawners have way too much health, slay the minions to get a bit of breathing room as needed, but beware, the boss can deal INSANE damage and may one shot even your strongest unit, it can deal almost 180 damage to a 100+ defense character.

After the boss you will get the Eternal Fruit, finish up whatever else you need to and return to the Homeworld to end the game, on the Homeworld there's a small altar in front of a stonehead, place the fruit on it to get access to the champion's room.

And I think that's about it.

thank you for this info, i was super confused when i got to the altar