I’m having trouble completing a lot of older content achievements because I need the bosses to trigger events during the fight but if i hit the boss I One shot kill them. How dose one do a lot less damage as to not kill the boss right away?
Soft foam sword toy is a good option. Usually one on AH.
You can buy the Soft Foam Sword from any toy vendor in your capital cities.
There are restrictions regarding its use though. It cannot be used inside instances nor can it be used against mobs that are non-trivial to you.