The Shinobi of the Moon (Possible Set)

[Hydra Iron Man]

 

This cards DEF is equal to the number of Monsters you control x 600. If this card is targeted for battle, you can switch this cards ATK and DEF until the End Phase. When this card attacks, it is changed to Defense position during the End Phase. When this card declares an attack, you can switch the ATK and DEF of this card until the End Phase. If this card leaves the field, pay 1000 Life Points.

 

I use old Yugioh Grammar. If you notice any flaws, feel free to remind me! Constructive Crit. is approved and graciously accepted.

[Hydra Iron Man]

Bump.

[Marco Polo]

This fits Casual section I think, unless you change it.

You're an old fun-deck player right? if so then you could use a look at today's standard archetypes to see what's powerful, what's weak, etc. 

Take a peek at Shaddolls for example: a really nicely designed archetype (in terms of gameplay, not balance), flowing, powerful, huge array of resources.

take a look at Infernoids, Burning Abyss, Yang Zings, Spirit Beasts, Artifacts, Nekroz. 

Take a look at the above archetypes to get a glimpse of how the game is shaped today, and design accordingly (there are also other archetypes currently dominating the meta but those should not be examples for you, satellarknights for bland gameplay and qliphorths for absolute brokeness)

 

This card's use-ability depends on the set you're making, if the sets is too weak - this card's DEF will hit 1800 at peak and that's nothing but a con.

Also worth mentioning is that destruction by card effects, and other ways of removal are *really* dominant today, ATK, DEF and battles don't cut it anymore - making this card halfway useless especially when you have to pay if it leaves the field. 

You could try downloading Devpro, an online yugioh game that'll quickly introduce you to all that's happening in the game today. good luck.