Yesterday I've made a theory about it, if you look at this image you can clearly see that it's not his own chakra, it's indeed a bijuu's - it has tails and TBBs, which are obvious trait of bijuu:
People who opposed this idea used as an argument that it's his own chakra, and Naruto is the same since he is Ashura's incarnation. But, in fact, its not like that.
Those people forget that Minato has absolutely same chakra mode, and he is Kurama's jin too:
Which leads us to the conclusion: the form of Ashura's bijuu mode is probably the FULL Kurama's bijuu mode, both Yin and Yang chakra together.
You must be registered for see images
People who opposed this idea used as an argument that it's his own chakra, and Naruto is the same since he is Ashura's incarnation. But, in fact, its not like that.
Those people forget that Minato has absolutely same chakra mode, and he is Kurama's jin too:
You must be registered for see images
Which leads us to the conclusion: the form of Ashura's bijuu mode is probably the FULL Kurama's bijuu mode, both Yin and Yang chakra together.