Actually not a meme :P

The synergy is having A Deal with Dark Ruler on hand, if you read it says " If a Level 8 or higher monster under your control was sent to the GY " etc, that means when you Link or Synchro off your Doomking, you will be able to get Berserk Dragon for free, special summoned from either Hand or Deck, ideally Deck. Since we can get Doomking out on the field very consistently, now it's all about drawing A Deal with Dark Ruler, but it's not necessary for the Deck to work or function.

He either helps you facilitate OTK's since he can attack all monsters your opponent controls or straight up use it as Synchro Material for one of the options you have on the Extra Deck. You can also play around with your 1st turn plays, if you drew A Deal with Dark ruler + Glow Up Bloom and any free extender, like Jack-o-Bolan or Destrudo, Berserk Dragon can act as an extra body that you can use to establish your end board with Scythe Locking your opponent or if you're going with the Formula Synchron instead, you could use Berserk Dragon with Formula Synchron instead of your Doomking, in case your Doomking didn't have the change to negate something that was important or crucial enough to use his negate on, especially if you managed to have a 2nd Dooming on board.