It gives each contestant a different power.
When Lucky has the exclamation point, he turns into a tornado, and throws all nearby players away.
When Eugene has the exclamation point, he flies into other players, and kills them on contact.
When Toof has the exclamation point, all other contestants turn into burgers. They die if Toof touches them.
When Lucy has the exclamation point, anyone near her gets flown away while she sucks any stars you drop.
When Lance has the exclamation point, he gets a Double Up. Lance gets a golden crown and everyone else gets purple crowns, meaning that any stars that other players pick up is only beneficial to Lance.
When Van has the exclamation point, his friends come and they try to help Van by whacking you for him.
Otto's special power is a multi El Vampiro, meaning that "ZZZ" symbols appear on nearby characters close to him. With the symbols, he is actually sucking all of his victims' stars up for his own benefit.