It’s a popular headcanon dude, no need to get angry. Peeps like a lil’ plus-sized representation. The reasoning comes from her being a seadweller and how a lot of seadwelling Earth creatures have that extra weigh for warmth and shit. Eridan doesn’t actually live in the sea so the same logic can’t be applied to him. But at the end of the day, peeps can believe whatever they like and it doesn’t hurt anyone so there’s nothing wrong with it. If you disagree, you disagree, that’s your opinion. It’s when you start telling others their opinions are wrong with no basis in fact or canon that things start to be not okay.

They probably flew there, peeps do weird shit when they’re high

Outside of Meenah, probably not. The were really only thrown in the comic as fanservice

He was poisoned by an archagent of Derse

This is explained in the faq

Homestuck is an interactive webcomic hosted on mspaintadventures.com written by Andrew Hussie and featuring several guest artists throughout the series.

That’d be the one that Gamzee killed post-retcon and pre-retcon respectively. 

She mind controlled Gamzee and made him steal it