Some events I thought of:
event.healing
event.starving
event.bossDefeat
event.bossDefeat(bossname)
event.drowning
event.hold(itemid)
event.lightning
event.burning
event.flying
event.teleport
event.kill
event.mount
event.mount(entityID)

These events seem obvious to me, but I'll explain exactly what I mean.
event.healing applies when natural regeneration applies, or when healing applies that is not a potion effect.
event.starving applies when taking starving damage.
event.bossDefeat applies for some arbitrary amount of time after killing a generic boss.
event.bossDefeat(bossname) is the same as event.bossDefeat except it applies to a specified boss.
event.drowning applies when taking drowning damage.
event.hold(itemid) applies when holding a specified item in your hand or offhand.
event.lightning applies when struck by lightning.
event.burning applies when taking burning damage.
event.flying applies when using some form of creative flight.
event.teleport applies right after teleporting, whether it be an ender pearl or an end gateway.
event.kill applies after killing any player, including yourself using /kill
event.mount applies when mounting a generic entity
event.mount(entityID) applies when mounting the specified entity.

I'm not sure if these events are posible, I already tried to make the event.burning but didn't worked very well because appears that this information is present on the server side only, I can get this from the server but the way the events works could lead to performance issues

Alright, I would appreciate if you would implement the events here that are possible without causing performance issues, if any. Also, thank you very much for taking the time to read through my feature requests and replying to them. I've just been cleaning up and organizing them because... reasons. I love the mod, and I also love that you are willing to take ideas from other people. Again, thank you.