OMG thanks for askin this I've been wantin to talk about it for AGES!! (I was gonna save for a comic/story but I am a rambler at heart pff)
OKAY so they first met when Mortis joined the cult!! Bob had already been a member for a bit atp and they weren't super close at the time. So when news came out that Mortis had supposedly died shortly after leaving the cult Bob wasn't too devastated.
Fast forward a few years later (I'd say a good 10 or so years?) and they meet again. Though they didn't recognise each other as Bob was in his costume and Mortis had changed so drastically he looked like a completely different person (plus, again, it was presumed he died). They get into a violent altercation after Mortis mistakes Bob for a demon, try to kill each other, but when Mortis accidentally unmasks Bob it abruptly stops the whole thing and gives Mortis a chance to run.
Unfortunately, Mortis can't stop thinking about that night in the following days because he was paranoid that Bob had recognised him (he didn't) and would inform the cult that he was alive. So Mortis had one goal in mind, and that was to eradicate Bob. Little did Mortis know that Bob had a similar plan in mind as Mortis was now the only person in town that knew he was the man behind the devil mask and was ALSO paranoid about being reported to authorities.
They eventually meet again, intent on eradicating each other, but one scuffle later they realise they harbor each others darkest secrets. They agree to keep each others secret identities under wraps. Out of paranoia they end up staying relatively close to each other, inadvertently giving them time to get to know each other more. The rest is history :3c (also this was getting long oops)
🥀: favorite thing about your ship? (Ouijabones)
Imma be self-indulgent and say it's the fact it's my silly Moloch selfship qwq
BUT ALSO I love the fact they're so drastically different but get along due to their shared curiosities and need to learn to navigate certain things together (such as Grim navigating the weird 'curse' they have and Moloch learning to navigate the human world lol. They help each other out!!)
🌹: is their relationship healthy, or more unhealthy/complicated? (Starsaviour)
I'm glad to explain either way man!! I just wanted to specify they were unhealthy from the get-go since I didn't want people to think I was romanticising cultist x cult leader and treating it like a silly fun ship
But yeah it is extremely unhealthy. Dia has a one-sided obsession with Skid's Dad and reveres him as her saviour. She assumes he reciprocates her romantic feelings but he's just playing along as it makes it so much easier to manipulate her.