I think both Hercules and Ioulas went into the different world to stop Ares. Ares's doppelganger was actually the God of Love in that world Hercules was married to Xena,I think and Ioulas was a jester,lol. The real Ioulas made it back along with his doppelganger,but Hercules and his doppelganger got stuck between worlds. Ares then sought Calisto and sent her back in the past to kill Hercules's mother, I cant remember how Ioulas got there.
There were actually multiple episodes of the mirror universe. The first was where our Ioulas got trapped in the mirror universe and helped the leader of the rebels, Joxer, defeat The Soveriegn (Hercules). The Soveriegn was poisoning Zeus with hynde's blood in order to take over Olympus, and thatr was causing our Zeus to slowly die as well. And he wasn't married to Xena, he was just boning her. He was actually going to marry Aphrodite in order to solidify his position as King Of Olympus (I think he was planning on killing her after their wedding night as well).
In another episode, both our Hercules and his doppleganger were trapped in between the two worlds. Then the evil god that impregnated Gabrielle, Dahok (spelling?) sends Calisto back in time to kill Hercules' mother when she's still pregnant, thus killing Hercules. Ares sends Ioulas back in time to try to stop her. He fails and follows Calisto to her reward, the chance to stop Xena from destroying her village and killing her family. Then he returns to a present where Xena had conquered all of Greece, as well as Rome, and is now a cruel and heartless emperess. Ioulas then uses the magic gem on top of Xena's royal scepter to travel back in time and give it another try. This time he does save Hecules' mother, and in the process Hercules as well.
There was a third episode with the mirror universe, but I think it was a Xena episode not a Hercules one.
I miss all these shows. Hercules, Xena, Conan, etc.
Space used to show them in reruns every day. Now almost all they show is Stargate. Preactically every time I tune in to Channel 45 all I see is Stargate SG-1, Stargate Atlantis, Stargate Universe, etc, etc. It's no longer
The Imagination Station. Now it's
The All Things Stargate Station. I also want to point out that here in Canada, you can get the complete series of both Hercules and Xena in two big box sets (one for each show) and they're available in stores. For those of you not lucky enough to live here in The Great White North, I suggest you plan a trip and come to visit. You should be able to find these box sets at HMV or Future Shop.