Whenever the "Big Bad" has you in a pinch, perform this friendship ritual to gain the strength, courage, and wits needed to kick his ass.
Friendship is a hugely recurring theme in Yu-Gi-Oh!. When still a loser-midget, Yuugi's greatest desire is to have: "Friends I can count on...! Friends who could count on me... No matter what...!! Friends who could count on me...!" (Takahashi) Then he gets the crap kicked out of him by a school bully in order to defend Jounouchi. Touched, Jounouchi gives Yuugi the last piece to the Millenium Puzzle (which he'd stolen from him earlier that day), allowing Yuugi to awaken his super-powered alter-ego and pwn all who stand in his/their way. In the process, Yuugi and Jounouchi become best buds for life. Not to mention, solving the Puzzle puts Yuugi in a situation in which he's never alone. Now he's got an ancient spirit sharing his body. He becomes great friends with him, too.
The Smiley Hand Circle of Indestructible Friendship first appears when Yuugi plays a Pilot Card Game with Kaiba. Anzu summons the boys and draws a "special sign" on their outstretched hands. Even when they're far away from each other, having grown up and departed ways, they can all remember this mark and gain ULTIMATE POWER!!1! Indeed, in his darkest moment, Yuugi looks at the ink on his hand and draws the exact card he needs to defeat Kaiba. Power of Friendship. Enough said.