Rage!Sans is a Sans in an AU that hasn't been created yet. Rage!Sans is one of the weaker Sanses in the multiverse. He can have a maximum of 3 Gaster Blasters out at once, and can't have an infinite amount of bones out either.
Rage!Sans has a pretty short temper and can be easily aggravated. Beacause he was aware of being one of the weaker Sanses, he decided to train harder than most others. This didn't increase his ATK, DEF, HP or LV. He realized that none of these things were increasing, but that just made him more determined to train harder. Then, one day, another Sans came to his AU and challenged Rage!Sans to a match. He accepted, but was fairly certain he was gonna lose. To his surprise, he didn't. He actually won pretty easily. The reason was that his SPEED had been raised ALOT from his training, so he was able to dodge every attack that came for him, and then delivered some very fast blows to the opposing Sans, and won.
Now, you might be wondering why he's called Rage!Sans, and that is because, when his temper gets to out of control, he goes into rage mode (Creative name, I know). This nearly quardruples his ATK, DEF and SPEED. His ATK and DEF weren't very high to begin with, but add that to his nearly unbeatable SPEED and you get an extremely strong fighter. It also increases his stamina by ALOT, making him able to use many Gaster Blasters/bones/any other attack at once. It will, however, cloud his mind, making destroying his opponent the only thing he can think about, even if it destroys an entire town. He's basically the Sans version of The Hulk. I wouldn't call him one of the strongest Sanses in the multiverse, but that is only because there are alot of Sanses that I don't know about.
When Rage!Sans is not in Rage Mode, he uses two bones as swords, or one as a battle staff. He thinks that if he always sent out Gaster Blasters and bones everywhere, he'd get tired faster and slow down, thus making him easier to attack. Instead he uses one or two bones, and focuses a bit to make these a bit stronger than normal bones. He doesn't manupulate gravity either, as this takes alot of his energy. He also hopes his SPEED will
When he IS in Rage Mode, he goes all out and uses everything in his power to stop his opponent. If he was fighting someone in Judgement Hall, and his first attack didn't defeat his opponent, he would probably destroy the hall out of rage. The only way to disable the rage is killing his opponent, tiring him out, (which will take a long time) or get Papyrus to do it. As clouded as his mind gets, Paps can always calm him down.