Guild Wars 2

The instance won’t let you replay, and I can find no data on what the achieves needed are either. How are you supposed to get mastery and the Abbadon’s Mask?

The only achievement for Rally to Maguuma is to complete it. If you’ve done it yet don’t have the achievement finished, I’d submit a ticket.

If you played it with a friend (who was instance-owner), you will have to replay it on your own.

As far as finding data:

https://wiki.guildwars2.com/wiki/Abaddon's_Cowl
https://wiki.guildwars2.com/wiki/Prologue:_Rally_to_Maguuma
https://wiki.guildwars2.com/wiki/Heart_of_Thorns:_Act_1

Good luck.