So it's sacrifice comes back with a 4800?

This has a 3 type of meaning of being destroyed The 1st of affect that you are currently focusing on is when “Red-Eyes Alternative Dragon” is destroyed by battle then you scan special summon any red-eyes monster from your graveyard 2nd part type same Thing except this part about effect: this means when a a card effect that states to “destroy” and “Red-eyes Alternate Dragon” was destroyed by card effect. Whether it’s in your hand or on your side field you can still special any other red-eyes monster. This includes if Red-eyes alternate dragon gets banished in process when “destroy” is in its text of effect (Side note if your opponent took control of Red-eyes Alternate dragon and they or you destroyed it, the effect of red-eyes alternate dragon is voided). As a reminder “Red-eyes alternate dragon” CANNOT use the effect on itself even if you have another copy in your graveyard. (Side note any red eyes monsters that’s been in your graveyard even if it has been there for the whole duel is still considered a potential special summon from the graveyard with “red-eyes alternate dragon” effect. As long as it has “Red Eyes” in it’s name.) 3rd Now for the main part of your question about the double attack (4800). It DOES NOT work work on any red-eyes monster except if you target is “RED-EYES BLACK DRAGON” from the graveyard to special summon it then its attack will double becoming 4800 ATK There is a way to get around that but that requires other cards which only works if you have them in play.