I'm ruling against this for my pcs who are trying to get rid of vecna and the fact that a lot of the stuff doesn't really align with being capable of doing it. So I'm confused on how this would work if at all
#PCs want to try and planar binding Vecna using magic circle and nystlus magic aura
rough bear
short merlin
RAW it unfortunately works, especially with 2024 rules that clarified that reading.
Basically Nystul's makes is so that spells treat that creature as another type (in this case celestial, elemental, fey or fiend) and thus Planar Binding can work.
There's a couple of caveats to this. First, Nystul's can only be cast on a willing creature, so they'd have to have dominated Vecna to accept it. Secondly, Planar Binding takes an hour to cast, so they'd have to have him sit in place for that long somehow.
If they can force Vecna to do all that, then they've likely won anyway.
Also, Vecna is a minor deity, so if it's an avatar Vecna can just.. stop controlling it. In a similar vein, even as a Lich he'd probably have contingencies to return to his phylactery if, say, he got mind controlled.
Lastly, as a DM you are well within your rights to just say they can't do it. This combo is pretty busted and probably not intended, no matter how much JC will tell you otherwise. If the players didn't communicate with you on this beforehand then that's on them for staking their plan on an exploit.
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Also also, if they want to get rid of him, the Imprisonment spell exists.
rough bear
RAW it unfortunately works, especially with 2024 rules that clarified that readi...
Yeah I don't see why Vecna wouldnt have plans to counter his imprisonment. Also idk if it changes anything but we are using 2014 rules in the current campaign
short merlin
You're the DM, you can say whatever
Vecna would be the ultimate Lich so a hyper intelligent nigh immortal wizard.
High level wizards should always have the Contingency spell on, with an elaborate trigger condition that would cover all possible cases where the wizard might be in danger / might become a danger to their goals / party. Then it casts like, Resilient Sphere or Dimension Door or maybe Dispel Magic. And that's just player characters.
Also, have a look at this video: https://www.youtube.com/watch?v=-2vbol24XlY
You can add as many or as few tricks from this as you like.
And that's all without really modifying anything in the statblock of a standard lich - and you've got Vecna to play with.
rough bear
My ass about to give him d door at will if these PCs keep trying to break the campaign through metagaming means
thin iron
RAW it unfortunately works, especially with 2024 rules that clarified that readi...
Additional element to consider: Vecna is one of the most powerful casters to have ever lived. With 2024 rules the way they are he likely has multiple reactions per turn, and can simply finger snap attempts to dominate away with counterspell, using legendary saves in the very rare cases the counterspell fails.
"Just dominate Vecna" is so laughably insane as a strategy that I genuinely propose the players try it and see what happens if the 2024 rules are being used here.
If it's 2014 rules, then Vecna will just throw chaff at them until their resources are spent. 
short merlin
At least that's what should happen, lol
funnily enough the module in which they presented vecna has like 5 minions tops and none in the actual fight
and the statblock itself is a joke to the recommended lvl 20
thin iron
(Oh, and, finally: Even if the players managed to actually banish him and all that, chances are, someone will unbanish him. There's always somebody looking for Vecna.)