Although it’s not a third Gremlins movie, fans of the franchise will be interested to learn that the Gremlins appeared in a 2008 TV ad for British Telecom. The special effects are 100% “old school” puppets and no CGI appears to have been used. You can check it out here.
Wikipedia claims that “[a] ‘Gremlins consultant’ was brought in to assist with the BT Gremlins commercial. Matthew Delieu who is considered to be the movies biggest fan provided original Gremlins blueprints and an original puppet during the production of the commercial and also puppeteered Gremlins in the 50 second advertisement. Delieu lives in the UK and owns many original items from the first movie including some original blueprints for Gizmo and original puppet designs.”
Interestingly enough, this isn’t the first time the Gremlins have appeared in an advertisement not related to the films or merchandise. Back in the 80’s, Gizmo and co. showed up in a public service announcement about drunk driving. You can find out more at this site.