Big fan of this one. Mainly for its simplicity and Flavor.
But i do see problems with it because of the game display system. half the time you wouldn't even notice this is out there.
a few possible solutions
1) Add a 1/1 prey creature to play for your opponent. Change name to Night Stalker. The Prey creature could only come into play via Night Stalker so you know theres a Night stalker out there.
2) When shade comes into play and opponent doesnt have a "tomb" give the opponent a "tomb" permanent. Tomb is a blank permanent that only reads "I never should have opened this". so first Shade out gives him a tomb there after you never really know how many are in play.
3) a gimmick condition that has to be met before the shade become invisible something as simple as "shade become invisible at the end of turn" It could still read the same its just you would see its in play the first turn its cast.
I also thought the attack value seems a little high when you consider eclipse... its debatable but where this is unseen/untargetable he should probably be more on par with Immortal
http://elementswiki.co.cc/cards-aether/immortal-elite-immortal/I might be a little conservative but a 3/1 for 3 dark and an upped 4/2 for 4 dark seem a little more on balance par imo. at the very least your upped 5/2 should probably cost more then the un-upped.
