So I just adopted a new pet from another user with the intention of turning him into a Bumbus, but when I went to the Blue Building the message it said was "You don't have any more pet slots". Does this mean I can't turn an existing pet into a bumbus?

You cannot turn an existing pet into a bumbus.

You can't morph an existing pet into a Bumbus. You have to use the Zapper or a Miracle Potion :c

Darn! Oh well. Thanks for the help you guys. c:

I'm pretty sure that yes, your only option is adopting them.

Made sense previously, since only colors could be applied to current pets, but with the Bhakoru it's now kind of out of place. Maybe suggest that the transformation option be applied to the Bumbus as well?

Not sure if you can zap for them, might be an (somewhat crappy) option... I would normally guess that you can't, but with things like Blacklight being zappable I'm not so sure anymore.

Edit: Super beat :c

Yeah, I'm thinking about making a suggestion of turning an existing pet into a Bumbus. Thanks for your help. c: