Minecraft has 60 Level Events (called Effect in Bukkit), documented for example here:

https://wiki.vg/Protocol#Effect

Bukkit only defines enum constants for 46 of those, without giving a developer any other way to send non defined or non standard effects:

https://hub.spigotmc.org/stash/projects/SPIGOT/repos/bukkit/browse/src/main/java/org/bukkit/Effect.java

The remaining constants should be added