>>55492000Ash-Greninja only existed because the anime's mandates were so rigid and inflexible at the time that the team was unable to give Ash a Mega Evolution to properly promote the games and merchandise due to the "Ash can only use Pokemon who debuted in that region" rule, which excluded Pokemon who were receiving Mega Evolutions despite technicalities. He also wasn't able to get Diancie later down the line because of the "Ash cannot have any legendary or mythical Pokemon" rule that was also present at the time.
So while they weren't able to bend the mandates a little to give Ash an older Pokemon that can Mega Evolve, they somehow managed to get a concession in the form of Ash-Greninja, a special snowflake "once in a million years" transformation that's BASICALLY Mega Evolution but also isn't. And then that backfired brilliantly when the "Ash cannot win a League Tournament or the anime has to end" mandate came into play and it got BURASTO'd, and it made you wonder how the fuck they got the OK to make Ash-Greninja outright.
Fast forward to today, now that L:Z-A is here, which is obviously going to rectify XY and ORAS' lack of Kalos Megas for Pokemon that aren't named Diancie, there is no longer a need for Ash-Greninja in the franchise. THAT is why Battle Bond no longer transforms Greninja in Scarlet and Violet.
