As spotted by PC Gamer, Redditor WickedSoldier991 has made a great discovery buried within the Halo Infinite multiplayer.
By making sure you're offline in Steam before launching the game, you can go to the Custom Games menu and access modes that have not yet been added to the online rotation.
PC Gamer's Wes Fenlon notes, for example, the new Attrition mode, in which each kill saves the team additional lives, all while a battle-royale-style danger zone shrinks the map as it goes.
Using these new game types as the basis for a custom template, you can then import them online to play with your friends in private sessions.
Be careful, however -- this doesn't seem to work every time, and there are problems with saving custom modes.
Multiplayer Modes Only Accessible Offline
- Arena: Attrition
- Arena: Attrition Dodgeball
- Arena: Elimination
- Fiesta: Attrition
- Fiesta: CTF
- Fiesta: One Flag CTF
- Fiesta: Strongholds
- Ranked: Elimination
- Ranked: One Flag
- Tactical: Slayer
- Tactical: Slayer Commandos
- Tactical: Slayer Manglers
- Tactical: Slayer Sidekicks
- Tactical: Slayer Stalker Rifles
