"Fusion Substitute" is a better choice than the normal "Polymerization", since all the material necessary for "Mobile Base" is probably on the board anyway, while the used "Pair Cycroid" can be shuffled back into the Extra Deck for card draw
This is a 5/5 not a 2/2 and this has no echo cost meaning it will happily stay in play and help you win
Silhouhatte Rabbit X LIGHT Link 2 [ Illusion / LinkEffect ] ATK 1500 DEF - 2 Effect Monsters If this card battles a monster, neither can be destroyed by that battle
Like most Magic: The Gathering cards, the value of Abyssal Nocturnus depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Guildpact)
In fact, Kyodai barely makes the list here since it only buffs itself and makes one other creature indestructible, barely scraping out Big Bad five color legends territory