For awhile, cards like Jace, Vryn's Prodigy were $100+ extreme outliers due to its power and prominence in that Standard format
In terms of gameplay mechanics, amethyst isnt as clear cut as the other colours in the trading card game, but typically revolves around providing players with either ways to benefit themselves or screw over their opponents
There are plenty of ways to double up on your instant and sorcery spellsmost notably Zada, Hedron Grinder, a commander who makes dozens of unplayable cards suddenly very strong
That last one isn't part of Odric's list, but it's still handy to have
I also really like Garruks Uprising
If one of the creatures is an illegal target and the other one isn't as The Earth Crystal's last ability tries to resolve, the original distribution of counters applies and the counter that would have been put on the illegal target is lost