Popular youtuber Thordan Smash leaked ingame play test video of the Crypto Heirloom.
It appears to be a sword similar to what you see Crypto's drone turn into during his default finisher.
This comes on the back of other play test leaks from an upcoming event Dark Depths.
To see the full video where Thordan Smash talks about the leaked heirloom animations you can view it here:
Most likely this heirloom will be available next season in the seasonal Collection Event!