It varies from betta to betta.. some 'enjoy' or don't mind company as long as there's enough places to hide and you keep the water quality up, and others will tear everything that moves to shreds.
♂ Nettlestung ♥ Pastel/Cellophane HM [RIP]
♂ Stormrunner ♥ White Marble dtVT [RIP]
♀ Willowisp ♥ Cellophane Marble VT [RIP]
♂ Skyshatter ♥ Butterfly Halfmoon [RIP]
♂ Starchaser ♥ King Plakat [RIP]
♂ Heartseeker ♥ Red/white DeT