Finn activated several abilities at once, elevating his physical abilities beyond what his body was capable of handling for a short period of time, causing his muscles to come dangerously close to rip with every move he made. Finn gambled everything on the slim chance of killing Athos quickly, or at least seriously injuring him and fleeing to where Emilia was.
They exchanged blows continuously, Finn advancing further and further, taking advantage of his superior speed to pressure him. Athos remained on the defensive, occasionally attacking while retreating one step at a time.
The dagger was clearly more powerful than his sword, cutting through slivers of mana with each switch, but Athos continually injected more mana and regenerated it. Finn took advantage of an opening in Athos' guard, piercing the dagger in the middle of his right hand and twisting it before pulling hard, breaking the hand and sending all of his fingers except his thumb flying.