18 if you also count out precogs.
But that is one of the time element's specialties.
Precog costs quantum. It can only be used in a rainbow or a time deck, both in which its cost hurt. This card costs nothing. It can't be compared to Precog.
/e: Your suggestion would goes in the right direction balancing wise, but I'd still see its sole purpose in decreasing the effective deck size.
What about making it actually 'op' - say, 20/20 for 10 
, guaranteed bottom of deck + 1 damage/turn while in deck? This would make a funny race deck.
Interesting... 20|20 may be overkill, but I can see where you are going.
The extra stats should be balanced cost wise based on the cost of (maybe based on 2
per card as estimate) it would take to get to one in a "standard" deck based around doing so...
24 - 7 = 14
14*2 = 28
Now we need to divide 28 / 6 to get the "average" cost each of 4.7
... lets round that to 5.
5 + 10 = 15
... also add +2 for upgrade advantage and you get 17
Lets use lighy dragon as a baseline
13 + 2 = 15
for a 12|12
12 * 17 /15 = 13.7 ... round that to 14
So it should be a 14|14 for 10
...
If you want to add in the 1 damage per turn as an extra 1 you could call it an 18
each instead... then you would have:
12 * 18/15 = 14.4 ... so maybe a 15|15 at the most.
