I have a kitten who has shown similar behavior. She is 7 months old. My husband and I had been noticing her being more and more aggressive with that "split personality" like you said. She would start biting, jumping, and attacking out of nowhere and then a minute later she would be all cuddly.
I had read that if the cat exhibits this behavior, like the biting or attacking, that you should shriek in a high pitched voice. I tried the yelling (in an angry low voice) and it would make her more aggressive. Before, she would go into these attacking spells almost once every day. Since I've been using this high-pitch yell technique, it has done wonders. Every single time I yell in a high voice she runs away and stops. I have been doing this for a few weeks. She hasn't gone into attack mode in a while. Anytime she goes for any type of bite, I screech so she learns. I think the cats attribute the high screech to pain. When they hear you screech, it lets them know you are in pain.
I would also suggest to not use your own body in play. Make a toy the focus of your playtime, not your hands.