As of M15, the letters for the rarity are printed on the card, C, U, R, M, next to the collector number and rare and mythic have a holofoil oval with the planeswalker symbol
But if there are some games you play a lot and the cards get shuffled, I think its worth it
However if they activate Droll after you have used Kaleido to send Sheep and Gold leo to add it back, you no longer have any way to access Wolf and therefore cannot continue to combo
The best element about this cycle is that they can fit into a whole host on existing and new strategies in Modern
In fact, Yugi used this ability in the anime to save himself from an attack from Obelisk the Tormentor , so its been put to good use