What the achievement asks
Aid six named characters during the Night Fae assault quest "Just Don't Ask Me to Spell It". Five points, account-wide.
All six can be done in one run, which makes this one of the better quest-gated pieces of On the Offensive. The catch is getting the quest to appear at all: it went months without showing up in 2021 and people were furious about it.
The six
You do this from the back of Krrprripripkraak, so nothing on the ground can stop you. Ignore everything, fly the route, and help the six.
Which button to press
Each one needs a different kind of help, and the game does not tell you which.
Target the character and read the debuff on them. That tells you which of Krrprripripkraak's action buttons applies: a healing wind for the wounded, a salty soak for the ones encased in stone.
The trap
The quest also asks you to help 25 allies. Do not let that counter reach 25 before you have found all six named characters, because they despawn the moment it does.
That is how most failures happen: people help everything they pass, hit 25 partway round, and then cannot find the last two anywhere.
If it happens, abandon the quest and take it again. The named characters come back.
Finishing the quest's objectives also dismounts you from Krrprripripkraak, which ends the run whether you were done or not.