WvW Duo
Thief/mesmer is a really good team up.
If you got a thief partner (with one of those insane damage builds, no kitten condition) you should try interrupt. You will almost be able to hear keyboards being smashed in frustration. Run PU or some armor with toughness because you will be one they go after. Check out the lockdown thread here on the forum, lots of builds there. I’d use one with staff.
Edit:
Here’s the Lockdown Thread:
https://forum-en.gw2archive.eu/forum/professions/mesmer/Guide-Lockdown-Mesmer-Tactics-Techniques/first