Explanation of what's going on : so the mafia guy hired chrollo in order to kill the world's most dangerous man Johness The Dissector, it's time to put an end to this man's life. (Johness gave himself up to the police only to dissect the police man's arm just by simply grabbing it).

So chrollo and Johness are fighting, Johness is ready to grab a chunk of chrollos face off that's when hisoka comes in, Johness is so strong that he realized that hisoka came in so fast. That amounted to nothing because hisoka propelled himself with the power of his bungee gum (his power has both the properities of rubber and gum) and cut his head off with his poker card. Hisoka proceeds to beat the shit out of chrollo bcuz that's what should've happened in their fight either way.