Crystalizer is an item in Adventure High.
While it's never been shown what it looks like, two things are known about it:
First, they are highly expensive upfront. Due to this, the Protagonist lacks one initially.
Second, they're required to obtain Gems.
To obtain a Crystalizer, speak to Molly in the Item Shop and she'll give you her old one, saying she could purchase a new one without issue. The Protagonist thanks her before leaving, causing her to say "Good luck!"