Now, I'll start off by saying this: Muka Muka is not terrible.  It's a decent card, and there are surely ways of playing it that make it shine.

 

However, I've seen people playing this card in American decks, and I've seen it do nothing but hinder them.  The entire strategy behind this card requires you to keep cards in your hand, which is the exact opposite of what you should be doing if you want to win.

 

A key strategy in Yu-Gi-Oh! and all other CCG's is board control.  If you have it, you're winning.  If your cards are in your hand and not on the field, they're cards that aren't helping you.

 

Muka Muka's attack is 1800 with 4 cards in your hand, and 2100 with 5 cards in your hand.  If you have 4 or 5 cards in your hand, at least one of them is good enough to play(if not, you need to tweak your deck!).  Additionally, even in America you can get cards like La Jinn and 7-colored Fish that allow you to deal 1800 damage without a thought.  If you really need to deal 2100 damage, either wait for it or use a card like the Landmine Spider(that's Jirai Gumo for you Americans).

 

The point is, one monster's high attack power will not win you the game.  Odds are that your Muka Muka will be knocked out by a Trap Hole or Mirror Force anyway.  Playing those Traps and Magics from your hand will help lead you to victory...and so will keeping Muka Muka out of your deck. ^_^