First, activate the effect of "D/D Swirl Slime" to send a card from your hand and "D/D/D Dragon King Pendragon" to the Graveyard to Fusion Summon "D/D/D Dragonbane King Beowulf."

Next, Summon "D/D Nighthowl" to activate its effect and Special Summon "D/D/D Dragon King Pendragon" from the Graveyard.

Then, activate the effect of "D/D/D Dragon King Pendragon" by discarding a card from your hand and destroy 1 Spell or Trap Card on the field.

Now, Synchro Summon "D/D/D Gust High King Alexander" using "D/D Nighthowl" and "D/D/D Dragon King Pendragon," so you can attack with both "D/D/D Gust High King Alexander" and "D/D/D Dragonbane King Beowulf"!