Dream Mentor

Crawl-through the cave entrance (quest minimap icon).

Talk to the fallen man (close the interface when it appears).

Starting with one of your 7 item foods, feed him 4 food while cycling through your different foods.

Starting with a food item of which you brought 7 items will ensure you do not run out of variety.

Talk to him again.

Feed him 4 more food as before.

Talk to repeatedly to raise his spirits:

Of the four chat options, choose the one that appears on the table below.

Select the response according to the table.

Repeat until a short cutscene plays and he sits up.

Feed him 6 more food.

Talk to him and raise his spirit as before until he stands up.

Exit the cave and climb up the ladder.

Or just use the Lunar Isle lodestone

Talk to 'Bird's-Eye' Jack in the bank. You will need 1 free inventory space for Cyrisus's chest.

Select the equipment he needs. The equipment is usually, but not always, dependent on your highest combat stats (Magic, Ranged, Melee):

Melee: Dragon helm, Abyssal whip, Ahrim's robe top, Ahrim's robe skirt, Ranger boots

Ranged: Splitbark Helm, Karil's top, Torag's platelegs, Adamant boots, Magic shortbow

Magic: Robin Hood hat, Dragon Chainbody, Black dragonhide chaps, Infinity boots, Ancient staff

You can use the NPC Contact spell to ensure you have the right equipment.

Return and talk to Cyrisus (Fallen Man) for a cutscene.

Right-click "inspect" and fill the remaining stats until he tells you that he is ok (if not already).

Talk to the Oneiromancer at the astral altar (most south-eastern part of the Lunar Isle) for a dream vial (herb).

Change your spellbook as necessary if you wish to use magic in the final fight.

Use an astral rune on an anvil (there's one on Lunar Isle in a small building to the south), then grind the shards. Add it to the potion.

Prepare for 4 fights (below level 100). Prayers and emergency teleports won't work. Neither will familiars.

Light the Ceremonial Brazier in the long hall building, near the lodestone.

Talk to Cyrisus (dismiss any followers before).

Do not click away of the chat or you will be teleported out

During the fight, you can leave at any time by using the pedestal.

Kill The Inadequacy

Kill The Everlasting (can safespot by the pedestal)

Kill The Untouchable (can safespot by the pedestal)

Kill The Illusive

Return to the Oneiromancer.

Quest complete!