Mismolts fall into two general categories: a molt where the mantis did not finish shedding its exuvia, and a molt where the mantis has somehow fallen before (or after) shedding its exuvia.
The first is self explanatory and is sometimes recoverable after its next molt.
The second is only reasonably survivable if the mantis still has its butt (or maybe a leg) in its exuvia and you hang it back up to finish.
If it doesnt shed its exuvia completely, the trapped limb is often lost at next molt. This just happened to a mismolted thistle I got for free.
Either way its bad, unless you hang them up immediately. Theyre so soft before the chitin sclerotizes, internal damage is a real threat. Joints dont articulate well. Tarsi lose functionality. Etc. Survivabilty is low, if they hit the hard plastic / glass deck of the floor.