The Pacifier is a weapon created by the villain Royal Pain.
This weapon shoots out a beam of energy. When the beam strikes a person, it de-ages that person back to being a baby.
The Pacifier was first created by Sue Tenny in Science Club, when she was a student at Sky High. The student yearbook from that year shows the entire Science Club arrayed aroung Sue, who is holding the Pacifier. Only a corner of the accompanying text can be read, but it appears to suggest that it has something to do with solar energy. Considering that this was a shool project, the Pacifier probably did not begin life as a weapon.
Text drawn from the Sky High yearbook:
"Here is the Science
winning solar w
These kids we
peting with som
clubs in the
Tenny is pre
that solar in