The bug here is that the tooltips show a called two-turn move as belonging to Silvally.After the failed Sky Drop on turn 12, the hover displays for moves get a bit odd. Silvally obtains a Sky Drop (5/5) and the enemy Venusaur gets a "Sky Drop" listing too, even though it was the victim.
(Normally, if Mew was to transform into something knowing (but not having used) Sky Drop, and then Mew uses Sky Drop, that would reveal that the Pokémon that Mew transformed into knows Sky Drop.)
We know about this. Hopefully my fix is close to landing!Synchronoise hitting Deoxys