DND_Reborn
The High Aldwin
My vote in case their creator doesn't chime in would be to move to engage Vecna (11 squares by my count as the default is to ignore diagonals and count them as just one square.).Hjalman's turn. (Reminder anyone who wants to can decide what Hjalman does)
Then take the Attack action for two attacks (via Extra Attack) and spend 1 ki for Flurry of Blows (2 additional attacks), allowing him to deny Vecna reactions. (EDIT: if the first attack hits, I would also activate Quivering Palm.)
However, I fully expect Vecna to use another reaction for Fell Rebuke.

I don't feel any rush for this, so I would allow the player 24 hours to chime in. What do you think?