Ojamas. Just because structure decks mean at least one card of support, and that would mean Ojama Pink would become real.
(For those who do not know, Ojama Pink is my theory on the existence of pendulums. Imagine Konami's card designing team. One guy says to his colleagues; "I bet I could make Ojamas broken with one card that still stays true to the archetype." They don't believe him. So he invents the entire pendulum mechanic, sets it up for a few formats so people know how to use it and everything, then creates the card.
Ojama Pink. 1000 defense, 0 attack. Level 2. PS 1-3. Spell: When this card is activated, add one "Ojama" card from your deck to your hand. Monster: No effect.)