I can't find much about him on the site, and the fan site really only says that he's from Atebus but works in The Darkside. Apart from his dislike of Ian Asmodeus and his somewhat-dodgy removal of his Pet Zapper competition, there seems to be a lot to know but not much opportunity to learn it. So:

1a. He's from Atebus. When? Is that where he's originally from, then he moved to the Darkside when Calvin Blackmoon took over Atebus, or did he move to Atebus after Blackmoon took control and he really only works in The Darkside?

1b. I'm assuming all this came about from a plot I wasn't here for, so is there some way to find out the storylines of old plots so I can fill in the back stories?

2. How dodge is dodge, really? Okay, so he's a bit lax with the experiment protocols, but there's a sliding scale from Mengele to Musk to That guy down the road who tests all his own chemicals. How harmed can pets get from his tests?

3. You think he's using the zapper to stay buff? He doesn't strike me as the gym type but that trim tum suggests some lifting is involved.

Which fan site are you on about? Maybe the zapper v2 used to be on Atebus (I think there's a trading card that also mentions it being at the carnival but that might have been the original zapper), but both zappers were moved to Darkside and eventually made into just one, I think the fragmentizer and crystal shop used to be in Delphi but they were also moved to Darkside. They're just retcons, I think.

I think information about older plots is lost, although I don't think him having used to be a Wyllop (yes that really happened) was a plot but instead just a backstory the staff made to justify why his original art had him as a Wyllop (which I can't find, I can only find items referring to it) and why he's a human (or human-like race) now. I'd like to know a bit more about that myself, I think it varies from staff member whether Ian turned him into a Wyllop by accident or if it was intentional. And he probably does use the zapper to make himself look more attractive, since when the zappers were combined into one, he said in the news post that he accidentally destroyed the other zapper when he was using it to make himself look better (just a lore reason for giving him a revamp).

Also, apparently Jim used to be a Charlie, but no one came up with a backstory for that, I think that was just a retcon.

Aiit, I think I'm allowed to link offsite on here, so the fan site is this one. It's the only one I've found when googling "subeta" + whatever term I'm looking for. If you know of any better ones I'm keen to know about them. That one above seems pretty bare, and I haven't been able to find a lot of information that I know should be available on there.

The idea that the details have been retconned makes a lot of sense. I've been a bit confused about the Wyllop thing because that fansite above does have a different image of Euclid that's more in line with the older style graphics I occasionally see on here, and doesn't have any images of him as a Wyllop, so I wasn't sure if that was his original form that they made ever-so-slightly more buff, or if his original form was the Wyllop, then that older style image, then his current one. I'll definitely bow to your superior knowledge on this one, particularly since you've been around roughly a decade longer than me, haha!