Kick the Dog: Ruffnut got Fishlegs sick with the flu, then carted him around town just to get everyone else sick For the Lulz. Even worse, she did it by punching him the stomach so he would wheeze on everyone.
One-Steve Limit: It's addressed that having Valka and Valentina means that there are two "Vals." Antonio has taken to calling Valka "Aunty Val" while Valentina is "Tía Val."
Out Sick: The Berk Dragon Racing finals were conveniently postponed after Ruffnut deliberately made everyone sick with the Flu.