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I would personally say to use the same tactics that you would if you were soloing an Thief... say, an Assassin. They have similar fighting qualities, only that an Assassin can Backstab/Poison, while the Jester can cast spells.
Getting the latest patch/reloading will get rid of the respawning enemies. However, you could also simply CTRL-Y the clone; I would say that you're justified in that.
For Mencar: I would say get Slow, Haste, Mirror Image, Stoneskin, and the essential stuff. Failing that, throw in a Fireball. But you have to do some damage to them. Use the Acorns to Dire Charm. The Moose can deal out damage decently well, though in my experience, it's best use is to try and take down the Thief as soon as possible. That Ring of Invisibility is very useful in hit and run situations. If you can manage to Dire Charm the Mages, use the MMM to pelt at Mencar, along with volleys of Magic Missiles. The fighters are easy to take on if they're Slowed and you have the Tuigan Bow.