Guys, listen to bored_ninja. The only insta-kill cards ever are Shockwave (two-card combo required) and Inundation (very situational, cannot kill Water creatures or Cells), and they will always be unless Zanz gets his brain brainwashed by aliens or something.
However, I really like the idea. So, since Earth is centered around HP, here's the change I suggest:
Ability to "Detonates: Deal damage equal to HP to next creature opponent plays, then die."
Stats to "0|20 or 1|20."
Not only will this change work better, but it's also far more realistic (I don't see a humongous dragon getting injured off one little mine, but I do see it being heavily damaged). With HevE armor or BB + Adrenaline (though this one's not recommended), it can almost anything. In a rainbow deck, it can also be coupled with Anubis to prevent CC. With this guy's cheap cost, Earth may have the CC it needs.