Arena Free-For-All Opening Gambit

[honeybunch]

My usually very regular five person group is down a man next week, so instead of playing without him our DM decided we'd have an arena free-for-all with our remaining players, as level 20 characters created for the occasion (and then maybe some arena combat against NPCs afterwards if we want to fill more time).

Anyway, we already all made up character sheets last week, and gave them to the DM, so I'm not looking for advice on how to build my character. I'm pretty new to D&D, however, and have never played a level 20 character before, so I'm hoping for advice on what might be effective opening strategies for the fight.

My character is an illusion wizard with 20 Int, Warcaster and Resilient (Con). I don't know anything about the other players' characters, other than that none of us have any magical items, and nobody is allowed to bring any summoned creatures into the arena with them other than familiars. Also, Wish and any similar spells have been restricted to duplicating spell effects. There will be three players there, so it will be me up against two other characters.

Right now, my plan is to start out by basically encasing myself in an adamantine block created by Major Illusion and Illusory Reality, then use the relative protection that affords to either True Polymorph myself into an Ancient Brass Dragon, or cast Simulcrum and try to get the upper hand that way.

Any suggestions on which of those strategies would be more effective, or any other strategies I might have overlooked?

[RulesJD]

Make sure your protective bubble is thick enough to resist getting Disintegrated.

Make sure you have it be a full sphere so they can't just burrow in from below.

After that, that's about it. Wish -> Simulacrum is the easy win. If they somehow let you stay in your bubble, come out with Contingency also up (Res Sphere if about to go below 1/2 health, etc).

Cast as many non-concentration buffs, so things like Blink and True Seeing.

Any class without higher level spell casting just trap in a solid Forcecage (one from each of you and Simulacrum). If you run into a Moon Druid (likely) plop a Feeblemind on them and then Ready Action -> Wall of Force sphere. Have Powerword Stun ready to take out the infinite Wild Shape Druid.

From there it's pretty easy peasy. Once you've locked down two of the other players, use the Wall of Force + Cloudkill (unless they are immune to Poison) combo with your Simulacrum to have instawin buttons.

Your only real threat is a very specifically built Sorcerer with Metamagic in which case you want to Feeblemind them asap.