My weapon suggestion is the Fire Axe. Looks like a modern utility axe, does the same base damage as the wrench, also does fire damage. Pretty simple and probably low tier, but I like the idea.
Sorry if its in there already (not the most original concept), but every time I try to use the gamemode to scroll through all the weapons the game crashes because it runs out of memory. Probably an issue with my laptop and not the actual game.
If you're also taking character suggestions, I have an idea, but all that info would probably just clutter up the comment section. I have ideas for all the Ultras and the Throne Butt and everything, but basically a character that can hold 3 guns instead of 2 with a trade-off of a lower reload time. I'm guessing it wouldn't be as easy to program as most other things, but if you think it'd be possible, I could talk about the rest of the character, too, and you can see if it'd be interesting enough.
(Edit: Hadn't seen the Robot Ultra Mutation yet, lol. I still think it'd have potential as a character, instead, though, so if you'd ever want to change Robot's Ultra, there's that option.)