See Challenge # 128.

"The depths of Ezan's seas contain enormous sea creatures that, luckily for Ezan's inhabitants, don't generally rise to the surface."

I don't think this quite works as a mechanic, but I wanted something like it to capture "large sea monster that doesn't want to be seen".

I'm not sure if this works as a keyword, but it seems like a fine one-of drawback.

Fascinating mechanic.

Thank you! I thought of it as a combination of blue's "can't attack unless" serpents, and illusion creatures which bounce to hand.

I agree, it's probably not broad enough to be a keyword, though if I remove that I may need to find another way to get the "doesn't want to be seen" flavour, I'm not sure it comes across.

Come to think of it, maybe it should just be "can't attack if defending player controls an untapped creature" (or controls two untapped creatures)?