Fixing a floppy Stormbreaker?
 

So I just nabbed the Infinity Saga Thor and Stormbreaker is really soft and floppy...I tried the old hot/cold water thing but it didn't help.

Are there any techniques for hardening soft plastic?

Lil blue pills. ;)

I keep those for myself :p

A few years back, Hasbro's BAF gladiator hulk's war hammer would eventually droop if Hulk held it by the... er... shaft.

One customizer drilled a hole and inserted either wire or a metal dowel.

The problem is hasbro's choice of plastic (soft, less dense plastic). A "cheat fix" could be to straighten a paperclip and glue or attach it to Stormbreaker's hilt (on the not-visible side).

I hear you though. I haven't had to deal with "floppy Stormbreakers" but instead Stormbreakers to thin to properly stay in Thor's hand (Figuarts...). For those I... take a small bit of poster putty and that holds the weapon in place "good enough" (with no permanent damage and still easy to remove).