@Valve kogata as in "small version" or "small form" or "small sized", not necessarily a dragon, could be a subspecies. Could also be a ko-doragon with ko as in small, but that would be shou-dora.
How a alchemist fight a dragon?
He can: Put it to sleep, poison it, make use of explosives, send one or more golem to fight it, etc.
Alchemists are chemistries that use magic... they are literally in control of how reality works by natural means...