On a scroll, mysteriously appeared overnight on a bed table:
Good morning, Miss Sunset Shimmer.
The being you are looking at is a changeling. (a pencil sketch of a changeling)
An equinoid eusocial emotivore shapeshifters, their main preferred food source is love and their modus operandi consists of replacing ponies.
(a graph, consisting of squiggly line with shaded area underneath, with dotted line slowly diverging up from squiggly line)
Statistical analysis of magical background tells us that they are slowly increasing their infiltration of Canterlot metropolitan area.
Direct observation suggests that in some cases, changelings may generate Love themselves.
(very shitty graph, consisting of fourteen very uncertain datapoints across four lines. Two lines run roughly parallel to each other, downwards. One runs well below them. One starts parallel to the two, but then may be bending up).
If you decide to accept this mission, Sunset, you must prevent changelings from causing harm to common pony and establish friendship between our races.
If you are captured or killed, Princess Celestia will disavow any knowledge of your mission.
This scroll will self-destruct in five seconds.
Good luck, Sunset.