A Monster of a Birthday. Give your guests a sneak peak of what's to come with Birthday Monster Invitations. Set the tone for a silly, spooky time with these monster mania birthday invites! 8 "You're Invited" invitations per package. Included green envelopes. Invitations are approximately 4 1/4 x 6. Spaces on the reverse side to write in party specifics such as "For, Date, Time, Place, Given By, R.S.V.P". Quantities Limited. Order now before they're gone forever! Show your birthday boy or girl how much you care with happy birthday stationery and favors! Stock up on the birthday party supplies you need to make this birthday an event to remember!