one good way is to sit outside the TMQ portal, and just ask people who come by if they need an extra person for their party. Usually they will say yes since its always good to have an extra person for a TMQ
You can create a party with just you in it. Just hit the party icon and create it yourself. That way you can still enter the portal alone. I tried soloing TMQ1 last night at level 25. I got to stage 3 but kept dying at the same part, i honestly think i can do it solo with more preparation: i was just trying it out last night to see what it's about.
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