Idea for Modeus' skill set if he'd lived to DMC5:
-Healing. We see demons heal one another in DMC5, and that demon guy Brad from the DMC anime could do it, so why not Modeus? If its just magic, he could probably learn it, right? Its probably more of a "lower class"/subservient demon skill, but still, Modeus could probably learn it. And Lord knows it could be useful.
-Shield/barrier magic. For himself and other people. Again, just support stuff.
-Ammo mods, for single people or the whole group. I keep thinking like Warp Ammo from Mass Effect 3. Just something to give his teammates a boost, if he really doesn't want to fight himself.
-Also kinda wanna give him Nevan, just because a) I doubt she'd be able to tempt him to anything*, and b) it'd be nice for him to have something to make up for his lack of wings.
[*= If Nevan even does that anymore. I doubt it? But it'd be nice to see her growing to like humanity as more than food, thanks to exposure to Dante and Trish. Maybe she, Modeus, and Trish could bond over being reformed demons? They get along because they both like human art and music- at least I assume so, based on Modeus' general vibe and Nevan's sunken opera house- and eat strawberry sundaes together. Its nice. 💜]
-Him and Credo (if he survived past DMC4) could make a good team. They'd need a lot of character development to get past their respective Issues(TM), but still, I think they could make a good team.