To kill catastrophe easily with 1 character only you need to get these on any sin/barb/warrior with 4.00 or 5.00 aps (dragon top mix works for sin/db, yes) while sparked
- Meridian full - you can get it for free at User Panel
- Genie with tangling mire and Enrage
- Gloom Sacred Stone and Quicken Sacred Stone (if sage)
- Abbadon Assault Potion (or an alt buffer barb for phy atk in case of wr/sin/duskblade)
These will ensure the Catastrophe boss dies as quick as possible
If you want you can also get Star Chart (with phy attack on bottom lines)
Ornaments that would help would be : DS neck or puzzle cube and warsong belt
Supreme or Ascended Supreme cape
If you got these then you can just make a R macro like this
and you are good to go
Tips
For the last boss i recommend having a dagger with holy stone in it to purify the amplify damage debuff
Skip the ball boss (white one, is after Hammer one) until you finish all other bosses (yes it can be skipped) and then do it since it might purge and you simply waste time on rebuffing then
You can lure Medusa out of the room with knife throw and if you get stuck, teleport on the hand that appears with Absolute Domain on