How would a level 20 Moon druid defeat a Forcecage?

Question

How would a lv 20 Moon druid get out of a Forcecage?

Some options I've considered are:

Repeated teleportation attempts

There don't appear to be any teleportation spells that would work from inside a Forcecage on the Druid spell list. The one that comes closest is Plane Shift, which can't send me to the plane I'm on so that's not good enough. Plus it's 7th level, so only somewhat "repeatable". Things like Tree Stride or Transport via Plants obviously won't work.

I've found only one magic item that might help, the Helm of Teleportation. Which has 3 charges. That should be good enough to get out of the first Cage, but maybe not out of the second one. Besides, does it count as metal armor?

Perhaps there's a Feat that can give me access to Misty Step? Would only be useful if I can cast it using spell slots.

Antimagic field or Disintegrate

Again, not on the Druid spell list. Any chance of getting access to this 8th level spell?

Answer 1

The feat Fey Touched is probably the best counter

Tasha's Cauldron of Everything introduced some new feats. One of them is Fey Touched. It increases one mental stat by 1, making it less costly for a Druid that wants Wisdom (or Charisma to have better hopes of teleporting out of the Forcecage), as well as adding some spellcasting options. A sample:

You learn the Misty Step spell [...]. You can cast [this spell] without expending a spell slot. Once you cast [this spell] in this way, you can’t cast that spell in this way again until you finish a long rest. You can also cast [this spell] using spell slots you have of the appropriate level.

This gives you access to the 2nd level spell Misty Step as if it was part of your spell list and always prepared. The first use per day is free, and then you can cast it normally. As a level 20 Druid, you have plenty of spell slots to cast 2nd level spells, making this option easily repeatable.

Honorable mentions with more limited uses

The Cape of the Mountebank is a Rare magic item that does not require attunement and allows you to cast Dimension Door once per day.

Multiple race options allow for some sort of teleportation:

• Eladrin: Fey Step is similar to Misty Step. Once per short/long rest.
• Shadar-Kai: Blessing of the Raven Queen is similar to Misty Step. Once per long rest.
• Githyanki: Misty Step once per long rest.
• Variant Human Mark of Passage (Eberron): Misty Step once per long rest. Also adds Misty Step to spell list.

Answer 2

See yourself out

A (mostly) sure-fire way to get out of a forcecage on your own, is to shapechange into a beholder^†. You now have a pointable antimagic field spouting from your main eye, however since it's a cone shape and only suppresses the forecage in its area, you'll have a hard time squeezing out. What you'll actually want to do is starting shooting at with your newfangled eye rays, until you get a disintegration ray on it.

If the target is a Large or smaller nonmagical object or creation of magical force, it is disintegrated without a saving throw.

Assuming the forcecage is fitted for your normal, medium sized druid body, you may find yourself squeezing in the confinement, but that shouldn't really affect you too negatively (outside the discomfort of having pressure on your many eyeballs). None of the medium sized beholderkin have a disintegration ray, generally to the relief of the adventurers who face them.

As this is a ninth level spell you'll only have one per day, but you are now a beholder and can turn your antimagic cone on the caster, preventing them from casting forcecage on yourself or anyone else. If you know you'll face multiple forcecage casters throughout a day, you'll either have to rely on your friends, or invest in ways to cast multiple 9th level spells per day, most notably either of the Epic Boons which let you do that.

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†: Our options for shapechange forms here are fairly limited; the common beholder is the highest CR beholderkin that is not undead, and employed as what you're most likely to have seen. Since shapechange doesn't give you the Spellcasting trait you'll need one that has a relevant "disintegrate" attack, or either of the spells as Innate spellcasting or similar. For Innate spellcasting, there are none with disintegrate, but aeorian nullifiers have antimagic field 1/Day. The woe strider from Theros also has conic antimagic field, but is CR7 (and cones don't really work, see answer). The astral dreadnought also has a cone, but is CR21 so can't be shapechanged to (and you may have an issue of size). If there are any relevant monster forms I've missed, I'd love to hear about them.