OK i have a Cyber Dragon deck with 3 the light hex sealed fusions. I Special C.D and Normal The Light. If I don't use Polymerization or Power Bond and use Light's effect, I can only bring out Chimeratech Overdragon and not Cyber Twin Dragon. If I do use Polymerization or Power Bond, I can bring out either one. I know Light's effect, but am I missing something?

I think you may have gotten your text a little mixed up there.

If you have The Light - Hex-Sealed Fusion and Cyber Dragon Face-Up on the Field you can use The Light - Hex-Sealed Fusion to Special Summon Cyber Twin Dragon but not Chimeratech Overdragon. This is due to Chimeartech Overdragon stating: Must be Fusion Summoned and cannot be Special Summoned by other ways.

If you have The Light - Hex-Sealed Fusion and Cyber Dragon Face-Up on the Field you can use Polymerisation to bring out Chimeratech Overdragon but not Cyber Twin Dragon. This is due to Cyber Twin Dragon stating: A Fusion Summon of this card can only be done with the above Fusion Material Monsters.

If you have a replay showing this working in the wrong way please post it so we can look into it.

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It does, that's why you can Fusion Summon Chimeratech Overdragon(1 Cyber Dragon + 1 or more Machine-type monsters). Like Steel mentioned, you need 2 Cyber Dragons in order to Fusion Summon Cyber Twin Dragon.

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Oh OK. Thanks guys. I feel the strong need to add Fusion Gate now