We Are All Made of Stars

Easy solo in The War Within.

Stand on one of the six little hexagons before the pull. Start the fight. Don't move. Kill the boss. (If you get punted during the fight, it's probably okay, just don't move off the hexagon on your own.)

Rygelon - We Are All Made of Stars
- Defeat Rygelon while the entire raid is affected by [spell=366195].
- Have all players stand in any one of these locations when pulling the boss.
- If done correctly, everyone will be transformed into a celestial and get the [spell=366195] debuff.
- Any player death will fail the achievement for the raid.
- New ability - Phase 1: [spell=366206] - Indicated by a small purple/pink swirly.
- New ability - Phase 1: [spell=366213] - Indicated by a large white swirly.
- New Ability - Phase 2: [spell=366231] - Indicated by a large white swirly.

Once you enter the room where the boss is, have the whole raid stack on the location shown on the picture below. (Probably works on any of the 6 spots)
https://imgur.com/a/00ogdNT

Once you pull the boss, you will all be transformed into cosmic creatures and you will have a debuff.
Play the fight as you normally would, nothing changes, that is all you need to do.
The negatives of this is that after each of the phases of the boss you will take slightly more damage.

If one person dies, everyone will lose the debuff (at least this is what happened to us, we didn't find any other things that made us lose our debuff, that includes getting hit by mechanics, and getting hit by avoidable things). The fight it not hard and I think this is arguably one of the easier achievements in the raid, since it only requires DPS and HPS and no additional setup or movement etc.

Happy achievement hunting!