it had something to do with samukai.
no he said in this place anything is possible that he said on episode 8.
Garmadon went to the netherworld and fought samukai. After a long fight Garmadon chopped off samukai's head and used his powers to combine himself with samukai's body and harnes the power of the netherworld in a spinjitsu vortex. Then he cast samukai's head out and on to the pirate version of Destinys Bounty.
Lord Garmadon got four arms by going a vortex and samukai vanished and lord Garmadon combined his arms with samukais using dark magic.