The last time I saw a poncho-wearing guy who liked to hang in high places to play the trumpet, he turned out to be the MAIN VILLAIN of the game duology.
(As a fun fact that you've probably already noticed, every time you talk with the trumpet guy in this game you can hear the first notes of Lisa's world theme :D)
Which is why I trust him as far as I can throw all the stuff he stood up on combined, including the stuff he'll be standing up on in later updates that aren't out, yet.
