It says "starts" invisible but your table is implying that it is always invisible.I'm not sure which is which.however, this being invisible for the entire time sounds really awesome.If it is invisible for the entire time i suggest changing ability text to this: Faded one is invisible to both players.Might be a little less confusing imo. maybe its just me, but "starting" implies that it starts out like that then on the next turn the effect has worn off.
Invisibility, I am presuming, would be removed by various cards, such as Rain of Fire and Pandemonium.Other than being interesting, it's not a game changer. It's essentially immortal, unless you're saying that it's impacted by field-wide events.
Lol Imagine a full invisible field of these and you're wondering why you can't play your pufferfish from your hand. OT - WHy such a defense buff for upgrading?
Regardless, you should probably drop the Upped Health to 6. It keeps it high enough to be blocked by Weight, but low enough to die in 4 turns to Thorny (providing 16 damage in the meantime).And if you wanted to heal it, ya shoulda played a different unit.
This passive could be interesting if it gained +X|+X when revealed, providing a sort of deterrent against revealing it. I think this would be better on a higher ATK and ~4 HP creature to avoid targeted damage and still survive Rain of Fire. Not a bad passive, but I feel this isn't a great example for it.