I would NOT recommend mixing species, as their skin secretions are different and are potentially toxic to one another. Also mantellas can be territorial which if there is different species together will lead to a stressed environment. Also painted mantella are in the process or have been placed on the IUCN Red list as endangered and the Mantella expactata is also IUCN listed as endangered as for the black-eyed I am not sure. Thus I'm not certain how easily one can attain these. I know that they are not allowing the exportation of the Mantella baroni anymore (and of course Mantella expactata is already not allowed to be exported from Madagascar).