The mechanics include: Transforming Double-Faced Cards - cards that can transform into a different card Disturb - Cards that can be cast from a graveyard that transform into a different card Meld - Combine two cards into one more powerful card Emerge - Sacrifice a creature to reduce the casting cost of the Emerge creature Madness - Cast the card for its Madness cost when the card is discarded Escalate - A modal spell where you can pay extra for each mode beyond the first Flashback - Cast the spell from your graveyard for its Flashback cost Investigate - Create Clue tokens to draw a card Blood tokens - Create Blood tokens to discard a card, then draw a card Undying - Return the creature to the battlefield with a +1/+1 counter Miracle - Cast the card for its Miracle cost if it was the first card drawn this turn Soulbond - Pair two creatures together for additional abilities Thats a lot, and on top of all those mechanics, there are multiple versions of the transforming double-faced cards

That is why the current pricing on Kethis won't change much in the near future
This is why proliferating them isnt a great strategy, as each instance of proliferate only gives you 1 counter
Well besides the obvious Gyarados and Ninetales listed already
Scroll of Fate The manifest mechanic, introduced in Fate Reforged , presented players with some interesting challenges
Each card has sentimental value to someone: where they got it, the deck it was a part of, that time you used it to battle so-and-so a lot of people tend to hang onto them because of the memories