A verification-first r2modman workflow for ULTRAKILL, from the correct Thunderstore community to a repeatable modded launch.
Start from the game’s own Thunderstore community, not a package with a similar name from another game. Read the loader requirement, target game version, dependencies, and recent package activity. r2modman support is a distribution and profile workflow; it does not guarantee that every package remains compatible after a ULTRAKILL update.
Make a clean profile and verify Settings → Locations against Steam’s Browse local files result. Install only the community-required loader or core pack, then use Start modded. A loader-only success proves more than importing a large pack and hoping the final screen identifies the problem.
Many ULTRAKILL mods change mechanics, visuals, weapons, or quality-of-life behavior. After loader startup, test the specific level or action named by the mod author. Reaching the title screen is useful evidence, but it does not prove a gameplay plugin is compatible.
Keep experimental gameplay mods in a separate profile and back up saves before testing packages that alter progression or level state. Use an unmodded comparison when diagnosing performance, input, or score behavior.
Clone the working profile before updating the loader or several mods. Test the clone, preserve the old versions, and move changes into the stable profile only after the same launch and gameplay checks pass. Record manual files that a profile export cannot reproduce.
A mod can be technically loadable and still be disallowed by a server, anti-cheat system, tournament, or game policy. For multiplayer, align required client and server packages and exact versions. Treat mod README files and server rules as primary operational documentation.
Confirm Start modded, loader output, dependencies, and the exact in-game trigger described in the README.
Some gameplay packages can. Back up important saves and test in a separate profile.
Prefer a documented package. If local import is necessary, record its source, loader, dependencies, and rollback steps.
Research note: September 13, 2026 snapshot. Game support and compatibility remain community-specific.
Recommended path: read this guide → download or create a minimal profile → record the result → expand to the full modpack.