Well, i can give some tips for keying/killing Paroxy for trying to farm the mount yourself.
1. Chief Paroxysmus is one of the hardest Peerlesses to key for. The Skull, Torso and Leg drops from Corrosive Slimes are rare and completely random (i've had 1 Torso, 3 Legs, and 6 Skulls before), and the Putrifier is a pain in the ass to kill without multiple chars.
What i do, is i use a Disco/Tamer with a 5 slot Najasaurus to round up ALL the creatures in the first bottom half of the dungeon, and get my Najasaurus to tank them all while running Consume Damage on him. I don't have my Najasaurus attack them at all, he just holds them. With 100% Poison Resist and Consume Damage running on him, the Naja is
essentially immune to the melee attacks of all those mobs, only their spells can damage him. While my Naja holds an army of Poison Eles, Acid Eles, and Plague Beasts and their spawn, i fly around on my Thrower and pick off the Corrosive Slimes and check them for keys, while occasionally alt-tabbing over to my Disco/Tamer to heal the Naja up.
When it comes time for Putrifier, i have my Disco/Tamer stand back running Consume Damage while my Najasaurus tanks him, i discord the Putrifier, and have my Thrower kill him from max distance.
2. Chief Paroxy himself is a no-Tamer fight, and he can hit for 120+ in a single attack at times, even against a Sampire riding an armored Swampy. He loves to suck attacking Mages into him and snap them in half with one of those hits.
I use a Swords Wammy on him. I ride a Paroxy Swampy, and use a 100% Fire Double Axe with 50% Lightning/50% HLA/81% HML/50% HSL/45% DI. I keep Greater Strength/Agility pots going with 50% EP to max out my STR/DEX. I'll Honor him, and try to separate him from his adds so i can Whirlwind them down. Once it's just him left, i'll cast EoO, Curse Weapon, Corpse Skin him, Onslaught him, and Double Strike spam, keeping Curse Weapon, Corpse Skin, and Onslaught up at all times. With Vamp Form+Curse Weapon, i have 70% Hit Life Drain, and my Double Strikes hit Paroxy for 250+ total, so i heal my entire 150 Health bar with every Double Strike, so even his occasional 120 damage hits aren't a big problem for me.