Can I use a crystal (amber I think to add a set affix) to add Plagued or Druidic to a wizards sword or glove?
Yes you absolutely can the specific crystal is amethyst 
Thanks! I wasn’t sure which CS it was but it would have been obvious in game 
Oh wait, so there’s no equipment restrictions for them then? Like plagued or Druidic can’t go on mana shields or gloves, etc…
Yup no restrictions any set affix that can be obtained through amethyst (some of them are class specific) can be put on any piece of gear
Right on. I assume you have some experience with it, so I have a follow up question…
When you use the crystal, I believe it gives you a few set affixes to choose from. In your experience does it often take a couple attempts to get the one you want?
In general it definitely can but getting it on the first try is common enough I’d say. The way it usually turns out would be ~3-5 amethysts to get what you want