If “Skill Drain” is active, this card is no longer treated as “Cyber Dragon”. You could not use it for “Attack Reflector Unit”, etc.
You can have 3 “Cyber Dragon” and 3 “Proto-Cyber Dragon” in your Deck and Side Deck combined.
If you Special Summon this card you can activate “Inferno Reckless Summon” and Special Summon “Cyber Dragon” from your Deck.
You can use “Machine Duplication” and “Proto-Cyber Dragon” to Special Summon up to 2 “Cyber Dragons” from your Deck.
While this card is face-up on the field, it can be used as “Cyber Dragon” for a Fusion Summon.
If “Proto-Cyber Dragon” is used in the Fusion Summon of “Cyber Twin Dragon”, and “De-Fusion” is used on that “Cyber Twin Dragon”, you cannot Special Summon the “Proto-Cyber Dragon” from the Graveyard because its name is not 1 of the listed Fusion-Material Monsters. (It’s no longer treated as “Cyber Dragon” while in the Graveyard.)