This is an easy Morphling for me, it was the coolest creature I recall ever seeing when it came out. The art is fantastic on the card and it was the inspiration for so many other creatures.
I have to give a honorable mention to a close runner up in Deranged Hermit though. He is "the" token creator and always will be.
It's more that you get the a creature out of the top 4, you get to sorta search for the land and play it (it's not taking the land drop even if you flip it that turn.). So yes its slower than Cradle but Cradle is ridiculously OP and even if it wasn't on the reserved list I doubt we would ever see it come back. They are trying to give you some extra value for that 2G upfront cost.
This is an uncommon buying it for say $1 or so is a far better deal than buying packs trying to open one. If they wanted to really make people opt for busting this card for their Tribal EDH decks they would bump it to rare.
It basically served as a minor distraction for players that might draft with it once or buy a pack on a lark but it had trouble selling a lot of product to people.
Sure they are pushing cat tribal a bit right now in Hour of Devastation and Amonkhet, but not having significant cats of note would feel like a flavor fail if Amonkhet block just passed them by.
You realize it makes tokens as fast as a Imperious Perfect right? Now elves are an easier tribe to get going, and Perfect does pump her tokens but they both generate 2 tokens every other turn, this card does it while spending less mana.
Actually the turn after this loses summoning sickness Perfect actually can only make one token and this thing makes two.
Well that and eventually they would have to start doubling back on released ones and release them again. I mean there is a lot of stuff they can do with these not on the reserve list but after 5-6 more sets of these you would likely go over a majority of the most notable cards.
This is definitely a tad overpriced, but i do like that it is far easier to cycle in most cases than Miscalculation.
There has been 3 completely black angels printed in magic before so yeah, already that has happend. White has had a couple multi-color zombies with black and Stillmoon Cavalier can be cast with just white mana.
At least we are exploring new design space with mana dorks and they are now allowing them to do other things besides tap for mana until they eventually get in the way of a large attacking creature to buy some time.