If an opponent is instructed to put a card into their graveyard without using the word "mill," The Water Crystal's second ability doesn't apply
Dont forget you can always pop them with Perlereino or Baronne, banish them with Fenrir or return it to the deck with Heartbeat or Kaleido: Rivalry of the Warlords : this is like the best one here, but they can end up in a board with Kaleido, S:P, and Grapha or even Rulkallos and Toad with a TKash as follow-up
Product Details [-2]: Look at the top four cards of your library
Thats not a lot of time to resolve the Rad Counter issue since getting rid of them is very challenging
Its effect is not hard once per turn, so if you summon another one you can use it again
Cards like Narset, Parter of Veils, and Hullbreacher (in formats that it's legal in) prevent your opponents from getting a new hand at all while you get a refresh