Hi,

I am wondering if these two events can be taxing on the papyrus engine ?

For example, if I was have a passive ability with an Onhit Event : Causes the player to lose X magicka, will this effect cause script lag if too many opponents are attacking the player ? And what about OnUpdate (Such as making a script that fires every 2/3 seconds to refresh a spell) ?

Not sure about OnUpdate but OnHit should be fine. I've used OnHit for lots of bosses in my mods. I use it for things like every 40 hits the boss receives the script plays the bosses laughter sound. Tested it with a bunch of followers and runs smooth as a baby's bum lol