You need to have the tf_logic_arena entity present in your map so the VSH plugin recognizes it's an arena map and starts the gamemode
Use vsh_ prefix in your map name to ensure that the bosses always spawn on the blue team, if you don't care about this stick with arena_
If you're planning to use custom music in the map, make sure you add a info_target named hale_no_music so the boss themes won't play while map music is playing
Other than that, it's like an arena map so you should know the basics of making one.
If you don't, here's a tutorial from @Crash on making one.
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