Right this moment, easily Cosmic Clone on Super Mario 3D Land for me. He is a shadowy duplicate of Mario. He mimics your every movement even when landscape changes though unlike their early version in Super Mario Galaxy 2, this one however does NOT disappear if you're hit by it. It simply continues to live on until you make the next fatal mistake.

He only appears in Special Levels fortunately which starts off with a maniacal high pitched laugh as he runs towards the screen.

I currently have 666 deaths total, yet I hardly see even the Statue Leaf or any other rare Power-Ups that show up if you suck at this game. I only see this rare power up when I'm in certain levels where there's a Cosmic Clone.

Yes, it's a villain.

To those who have played, do you agree? Does Cosmic Clone a product of Nintendo's artistic genius or is this indicative of Nintendo's real laziness to create a proper villain?

Waluigi is an indication of Nintendo's laziness to create a proper villain but since the Cosmic Clone's purpose is too do exactly the same thing as Mario only a second later, I think the character being a dark Mario figure fits just right.

I haven't played Super Mario 3D Land but in Super Mario Galaxy 2, the Cosmic Clone made for some really interesting (and somewhat frustrating) challenges.

The Cosmic Clone is easily the most frustrating thing ever. Even in levels that don't become hard with him, they are still not fun at all. The star coin placement becomes things along the path anyway (no time to explore) and in many cases, I didn't even really go all that fast (based on the completion time) but still kept making mistakes just because of the stress the clone causes.
What I ended up doing is every time I encountered one of his levels I would always go back and get a leaf and then save spam it. Since he matches your speed, the slow downs when you hover with the leaf affect him too, which gives you time to think and properly plan the next movement. Lakitu in Mario 3 was bad, but the clone is so much worse.

Dunno about 3DLand but the cosmic clone on Flip Out galaxy for SMG2 was certainly a tricky beast.

I suppose Waluigi would take the crown. Perhaps, Cosmic Clones' simple character design have to be taken for what it is. Any more modification would have either increased the difficulty even more, or worse breaking the game's balance.

It still does take some getting used to, and the 3D landscape does add challenge to the game as a minor shift in the analog stick could mean death.

I also believe the 3D feature is oftentimes not beneficial.

I think they're the product of neither artistic genius nor laziness. I think they're the frustrations of Nintendo developers given form.

I didn't think he was that annoying or challenging, to be honest. You just have to make sure you give your self enough space/ time to not get hit by him. I think I have less than 100 deaths in 3D Land... The real challenging parts are the dare devil runs on smg. You get hurt and you die. Much harder than cosmic clone imo.

They need to give Bowser an alternative motive that doesn't have anything to do with stealing Princess Peach and taking over the world (or universe)

You can always circle arround and the Cosmic Clone won't hit you. I used that trick when i needed some precise jumps.