Player A sets 3 cards to field.
Player B's "sharp eyes" spots set card abit bendy bendy
Player B thinks: "ZOMG! Set shiny card is Starlight Road/ Torrential Tribute/ Mirror Force/ some expensive shitt so next turn i activate MST to destroy it"
Player A: "Hahahah thats MST I chain it back hit your Black Whirlwind muahahaha cos my MST is foil version!"
Player B: WTF
Moral of the Story: Use foil cards.
Yup, its a dog eat dog mentality of Malaysian duelists all right, true story