Cyber Phoenix will only negate an effect if it targets, and if it targets only 1 monster, which is one of your machine monsters. It would therefore negate Sakuretsu Armor if used against one of your machine monsters. It would not stop Icarus Attack, which targets two monsters. It doesn't matter if it only targets one of your machines, it is still invalid due to targeting two monsters in total.
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No, there's a difference between a 'Blue-Eyes White Dragon monster' and a 'Blue-Eyes White Dragon'. The first is any monster with "Blue-Eyes White Dragon" in the name, while the other is a card called, and only called "Blue-Eyes White Dragon". Blue-Eyes Ultimate Dragon requires Blue-Eyes White Dragons only, not any variant. Likewise, Cyber End Dragon looks for "Cyber Dragon" not "Cyber Dragon monsters". You can only use cards called, and only called "Cyber Dragon". Note that Proto-Cyber Dragon has a name-changing effect that makes the card name into "Cyber Dragon" so does count and can be used for Cyber End Dragon. 'Cyber Dragon Zwei' also has an effect that also changes its name, though you need to pay a cost to do so. The whole point of these name-changing effects is so those cards can be used with Cyber Dragon's support cards, they would not normally be able to do so because they are not called, and only called "Cyber Dragon". Having Cyber Dragon in their names is not enough, as has been explained above.
No, "Versago the Destroyer" cannot be used as a Substitute-Fusion Material monster in the Fusion Summon of "Cyber Twin Dragon". "Cyber Twin Dragon" specifically states: A Fusion Summon of this card can only be conducted with the above Fusion Material Monsters. This card can be Special Summoned from the Extra Deck using "Cyber-Stein" or "Metamorphosis", but if it is Fusion Summoned, two "Cyber Dragon" cards must be used. The closest you can get to a Substitute-Fusion Material monster for "Cyber Twin Dragon" is if you have "Proto-Cyber Dragon" on the field. (It's card name is treated as "Cyber Dragon" while on the field.)
No, Backfire only triggers when the Fire monster is Destroyed. Tributing a monster does not 'destroy' it.
If a card looks for a specific number, it will say so, ie, it will specifically say "one" monster. In this case, the opponent has 'a monster', if he has one, two, or even five monsters on the field. So just as long as they've got one or more, and you have none, then you can special summon Cyber Dragon.
No. Skill Drain only works for monsters already present on the field. Any effect that activates in the hand or graveyard are not negated by the effect of Skill Drain.