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.
"Glacial Chasm"
Type: Land
Cumulative upkeep-Pay 2 life.
If Glacial Chasm would come into play, sacrifice a land instead. If you do, put Glacial Chasm into play. If you don't, put it into its owner's graveyard.
Skip your combat phase.
Prevent all damage that would be dealt to you.
T1
Balance?
Channel?
Demonic Tutor?
Regrowth?
Legacy
Sinkhole?
Mana Drain?
Hymn to Tourach?
Extended
Burning Wish?
Duress?
Standard
Cruel Edict?
Pyroclasm? (if you can grow him)
Rampant Growth?
Didn't notice it had to be copied on the stack that does weaken it tremendously