Ben 10 season 4 episode 2 : Divided We Stand

During a trip to the beach, Ben discovers a new alien on the Omnitrix, Ditto. Ditto has the power to multiply at will, drawing the attention of Dr. Animo, who has just escaped from prison with the help of a mutated seagull. He captures one of Ben's Ditto clones in hopes of exploiting his alien DNA for his own evil purposes. Using the alien DNA, Animo creates an army of self-multiplying mutant Stinkflies, but Ben exploits the inherent weakness in the clones to destroy every Stinkfly clone and capture Dr. Animo once more.