I have boss slayer on my main account and when my alt used a key that don't have boss slayer we were able to stay in the fight till all keys were used up.
thin iris
I have boss slayer on my main account and when my alt used a key that don't have boss slayer we were able to stay in the fight till all keys were used up.
weary sparrow
Afaik this is an intentional feature, its been established that if one person in the combat group has boss slayer it works for all members participating (even if the key-holder doesn't have the boss slayer upgrade)
cerulean nacelle
it is indeed not a bug