This is Victor possessed by Rebellion, and Billy with all the abilities he’s ever shown to have copied.
Victor through his negation power Undead, possesses a wide array of regeneration-based attacks including stuff like: a hardened blood blade, a long-range pressurized blood slicer, shooting off his fingers and having said fingers regenerate into clones of himself that can attack on their own, and a giant wave of blood that looks like a DBZ beam attack. His regen is based on the the idea of conceptually negating his own death, and is high-end enough he can come back from a blood puddle, as well as survive the destruction of the planet Earth. Separate from his regen, Victor should also possess a degree of soul manipulation as his alternate personality (Andy) gained control of his soul so he could move it separately from his body and use it to fight alongside him or imbue it into his katana. This ability was used to attack a being that could switch between being physical and astral/spiritual at will by attacking at both levels at once (meaning Andy/Victor can slice the soul along with the body).
Rebellion is one of the three sacred spirit treasures created by one of the two gods of the UxU verse (Luna) said by her to be capable of killing the other god (Sun). 
Juiz has rebellion possess her sword and we see she that with it she becomes able to stagger Sun 
, and pierce its body 
. When Victor has Rebellion possess his body he goes through a transformation and gains the power to generate a massive blood beam that can knock Sun into the air off his feet 
. To put this into perspective Sun is fast enough to send an attack from his back all the way around the planet in seconds to counter a negator who negates the concept of movement (as he can't stop the motion of what is outside of his visual range) 
and is durable enough to tank the force of his own attack when he crashes into Earth and obliterates it 
. And while not as impressive, it's also worth mentioning that Sun simply standing up straight causes destruction that can be seen from space 
.
Billy has multiple powerful haxes. To explain i'll take from the wiki and add some of my own further explanation for context
So how far does this duo get against the OBD's favorite punching bag?
Victor through his negation power Undead, possesses a wide array of regeneration-based attacks including stuff like: a hardened blood blade, a long-range pressurized blood slicer, shooting off his fingers and having said fingers regenerate into clones of himself that can attack on their own, and a giant wave of blood that looks like a DBZ beam attack. His regen is based on the the idea of conceptually negating his own death, and is high-end enough he can come back from a blood puddle, as well as survive the destruction of the planet Earth. Separate from his regen, Victor should also possess a degree of soul manipulation as his alternate personality (Andy) gained control of his soul so he could move it separately from his body and use it to fight alongside him or imbue it into his katana. This ability was used to attack a being that could switch between being physical and astral/spiritual at will by attacking at both levels at once (meaning Andy/Victor can slice the soul along with the body).
Rebellion is one of the three sacred spirit treasures created by one of the two gods of the UxU verse (Luna) said by her to be capable of killing the other god (Sun).
Billy has multiple powerful haxes. To explain i'll take from the wiki and add some of my own further explanation for context
- Unstoppable: Billy has copied Top's Unstoppable, allowing him to move at high speeds (for reference Top is able to run around the Earth and accelerate to become faster than light).
- Undead: Billy has copied Andy's Undead, allowing him to regenerate from severe damage (mostly the same usage of the ability as Victor/Andy though less versatile due to inexperience with the ability).
- Unjustice: Billy has copied Juiz's Unjustice, allowing him to negate other people's sense of justice. (This can for example force someone who's vision of justice is survival to commit suicide).
- Unmove: Billy has copied Chikara Shigeno's Unmove, allowing him to negate other people's movement. (Anything or anyone in the visual range of the user is put in complete stasis because motion gets negated conceptually)
- Unbalance: Billy has copied a certain architect's Unbalance, allowing him to negate the balance of buildings. (fairly self-explanatory)
- Unchange: Billy has copied Gina's Unchange, which he uses to create invisible barriers from unchanging air. (can be shaped into giant telekinetic hands sort of like Elfen Lied)
- Undefinition: Billy has copied a certain negator's Undefinition, allowing him to negate the definition of things, including Blood's shape (good for removing barriers potentially)
- Unruin: Billy has copied Ruin's Unruin, allowing him to recover from being damaged. (Similar to Undead, another high-end regen ability)
So how far does this duo get against the OBD's favorite punching bag?
ha
