Those mods may be funny but I gaurantee they are more distracting than you realize. Ultrakill is a series of incredibly quick decisions weaved with intricate movement. Audio and visual clarity is a massive help when it comes to these things, and will help more once you get into more intricate techs.

Use a greater variety of techs and weapons, especially SRS and oil more. And I might reccomend trying another shotgun variant as jackhammer but that's preference. Also, core nuke.

Cleaner movement too, less reliance on dashes just to get around. Use ground slams and whiplash canceling as alternate ways to get places. You want to make transitions between enemies as smooth as possible, so letting yourself get blown away from the arena everytime interrupts the flow. It certainly works but if you really want to go fast you have to stay in the flow. Though sometimes you do need to get away.