Nearly all submissions are done electronically these days. When hard copy ms were submitted you had the option to also send self addressed, postage paid packaging for the return or just a self addressed envelope for your rejection/acceptance to come in. Very few agents will rep children’s picture books because the payout is so small. 15% of just a little bit is a really little bit.
I don’t know about characters in comics but I do about those in regular fiction. Sometimes they have a lot more free will than the fiction writer would like.
Actually, when you thought you saw John Wayne doing something like that it was really Yakima Canute