Lightning Ironwolf with the right gear is an amazing support: Plague, Griffons, Viperskin, eth Spirit Monarch nets you: Cleansing Aura (very useful for physical damage heroes!), Lower resist proc when in trouble, 1-3K lightning damage, frequent static field, 86 FCR (second highest breakpoint).
Fire Ironwolf wielding Spirit, Flickering Flame, Ench/FB Ormus or Viperskin, eth Spirit Monarch) nets you: approx. 250+ fire damage enchant, 86 FCR, 3k+ Fireball, fire resist aura.
Fire Rogue merc wielding Mist (GMB or MB), Hustle armor, Flickering Flame nets you: ~165-220% ED for the party, 1200+ fire damage with 100% pierce (shreds Wraiths and Wisps), fire resist aura, 11 fpa (GMB) or 9 fpa (MB, second highest breakpoint!) without Fanaticism, Inner Sight (circa -1800 defense to monsters).
Barb merc wielding any weapon for example: Grief, Plague, Hustle, Frostwind, Azurewrath, eth Death/Oath, Last Wish etc AND Lawbringer, Hustle armor + any life leech helm nets you: massive damage vs. undead, Decrepify proc and whatever the primary weapon has to offer, high attack speed and AMAZING run speed.
All of these are able to deal with PIs on their own in a two player game!
Side note 1: A single point into Berserk should deal with any PI that is not immune to magic damage!
Side note 2: Atma’s Scarab is BiS for a pure Strafezon!
Side note 3: The Barb merc with Grief+Lawbringer makes short work of all Wraiths, Wisps, Dolls and Oblivion Knights, which are among the most annoying and dangerous enemies in the game. Don’t forget: The Sanctuary aura affects BOTH weapons, so two Lawbringers are a waste in my opinion.
Good luck!