This is it. This is where the Ancient will appear to lay our world to ruin. All I have to do is incant the correct banishment ritual with the invading god's rune, and the madness ends. - Examining the Banishment Ritual.
The Banishment ritual is a four-rune spell needed to banish the Invading god.
Obtaining the Banishment Ritual
To obtain the banishment ritual, the player must complete Dungeons, where they will receive either a hint about one of the three gods, or a piece of the ritual. The ritual itself consists of four runes, three of which are fixed. The last remaining rune will be the rune that denotes the god you are trying to banish. The player does not necessarily need all four pieces, as you may have found the three fixed runes. In this case, as long as the player knows what god they want to banish and what rune belongs to that god, they may safely cast the ritual.
Casting the Banishment Ritual
Once you are ready to cast the Ritual of Banishment, head to Stonehenge. Once you are there, enter the dungeon there and you will be prompted to find the underground ritual chamber. This chamber can be accessed through a semi-circle shaped opening with ladder in it near the floor. The entrance to the chamber is always behind a locked door. Once you are in the chamber, cast the Ritual of Banishment as you would any other spell. If any of the fixed runes were incorrect, you will suffer a heavy sanity penalty. If you cast the spell correctly, you will be transported to a realm where you must fight the Ancient.
Fight The Ancient
When you are drawn into the Ancient's Realm, you will have to physically and magically battle it. The ancient will attempt to drag itself towards you by sprouting tentacles which it uses to anchor to the far wall, closing the space between it and yourself. As well, it will spawn monsters, usually only one kind of the lesser monster types.
You can counter the spells the same way you counter the Cultist's magic, by casting the same runes back at it, which will push back the Ancient's main body mass. In the meantime, you need to physically beat back the tentacles. Troughout the fight, disembodied eyes will appear which will cause the screen to become filled with static, heavily obsucring vision. Shoot or strike the eyes as soon as possible. Whatever you do, do not try and physically attack the main shadow mass, as coming into full body contact with it will result in an instant death.
Eventually, as you push the Ancient away, the opportunity to cast the Banishment Ritual comes up again, and you need to cast it a second time. This will defeat the Ancient for good.
Depending on your Sanity level, you will get either Ending A (Victory) or Ending B (Victory - Insane). If the Ancient kills you, you instead get Ending C (Ultimate Sacrifice). Try to enter the fight with as high of Sanity and as many bullets as you can manage, as this will help make the fight easier.
Casting the Wrong Rune
- Should you Banish the incorrect god, this results in Ending D (Mistaken Identity) and a game over.