Can i get reactor by using the amythest crystal? Or it’s rare?
No you can’t get it by amethyst so it’s a rare
you can roll it with Amethyst, but only on Wizard Items. so Warrior & Rogue would have to use a Wizard Item to roll Reactor onto then Jasper it to their Class, or Jasper a Warrior/Rogue Item to Wizard, roll Reactor onto it, then Jasper it back to Warrior/Rogue.
when Jaspering back and forth between Classes, Talents and Talent/Skill Affixes might change to the original base affix that is found on the original base item, usually based on the Talent Tree. yes, I have had to spend extra Crystals to fix this problem, but a good Farming Build means you should have enough Crystals to fix a problem like this with.
here is a post that lists many Set Affixes that can only be rolled with Amethyst onto Items of only one Class.