THE CONTEST IS OVER!

Don't hate me for this, but here's how it's figured out:
During your opponent's draw phase if:
((your grave % your decksize) / their grave) >= ((their grave % their decksize) / your grave)
Then the monsters undizzy.

The other things were obviously having a constant attack modifier equal to your hand minus theirs, and life until end of turn at the beginning of your turn equal to your mana minus theirs.

At the end, I accepted any answer which included a combination of deck and grave compared to the opposite combination of deck and grave, since it was those values it was based on.

Congradulations to:
Kaddar
Chichiri
Leander
Shiv
Play
Bahumut_clef
Nounou
Hello
AeonEX
masamunemaniac

For figuring it out close enough.
They will receive a special card of legendary status once the card is created.

However, to show I'm not evil, I've decided to give everyone who sent in an entry a different, less legendary card, once that card is completed.

These are the people who entered:
Kadder
Chichiri
Leander
Shiv
Play
AeonEX
Hello
Nounou
bane2571
Spork
Prince of Halfwits
Squirm
Bahamut_clef
Unknown
masamunemaniac
Whomper
Aristodrim
Lunar Knight
Anifan99
Xellina
Shabbydew
ViciousChicken
Rick Sim
Amped08
azulknight
cheesus
Ultros
Astral Dragon
Tamdrik
EffullBao
EDIT: Inugami got in just under the deadline
EDIT: missed akujintails
EDIT: Missed Eval Evin too

Sorry for making it so hard, I didn't mean for you guys to lose sleep or sanity over it. But now the mystery of the cake has been demystified, and you can all relax.