The spell Forcecage allows you to create a prison in the shape of either a cage with bars, or a closed box.
Escaping the Forcecage is (obviously) meant to be difficult:
A creature inside the cage can't leave it by nonmagical means. If the creature tries to use teleportation or interplanar travel to leave the cage, it must first make a Charisma saving throw. On a success, the creature can use that magic to exit the cage. On a failure, the creature can't exit the cage and wastes the use of the spell or effect. The cage also extends into the Ethereal Plane, blocking ethereal travel.
However, if you choose the cage shape, it is ridiculously easy to escape, using one of the following means:
- Wildshape into an form that can squeeze through 1/2 inch gaps
- Polymorph, True Polymorph, Mass Polymorph, Shapechange or Animal Shapes, similar to Wildshape
- Gaseous Form, can squeeze through any gap. Maybe also Wind Walk, but that spell doesn't explicitly mention being able to squeeze through gaps.
- Antimagic Field: Forcecage is only immune to Dispel Magic, not Antimagic Field. Would also work on a box-shaped Forcecage.
- Disintegrate, which can destroy creations of magical force. Would also work on a box-shaped Forcecage.
- Casting Misty Step a bunch of times, since it's just a 2nd-level-spell and you're likely to suceed on the Charisma save eventually.
So, in the end, Forcecage with its cage shape seems like it's most likely a waste when used on a caster, especially a druid. Do note that Antimagic Field and Disintegrate are included not because they are especially easy, but for completeness, and to illustrate the wide variety of ways that one can escape a cage-Forcecage.
Is escaping from it really as ridiculously easy as it seems? Or am I missing something?