Can I mix a beta fish with..?

A lot of ppl including petco/petsmart ppl have told me betta fish cant go w anything but from my own experience i can tell u that female betta can go with nething other than another female betta (the bettas that dont have long fins) the beautiful long finned bettas are male they r way more territorial. right now i have a male betta in a 5 gal. tank w three mollies were goin on 4 months theyve all been in the same tank. i had a male betta that i kept in a 10 gal tank w some run of the mill goldfish, a spotted danio and a barbfish. it killed them all within 2 days. personally i think male bettas vary a little some r more tempermental than others. but if u have ne doubt puttin all these fish together dont bcuz the betta wont attack the other fish until no one is looking n by then ur other fish wil b dead. worse case scenario is the betta can go into some other tank they have 4.95 betta tank at walmart its like 5 gal n it comes w a divider for another betta fish. but i wouldnt recommend a second betta 4 that tank