I just got a request to do an Avengers cake and wants it to look just like the picture she sent me.. I don't think i have ever been stumped by a cake like this.. Can someone please help me identify what technique was used to do this cake? Transfer sheet maybe? Picture is attached! thanks!!

Since that is a copyrighted cake make sure that you get permission to use those characters since you will be selling the cake.  You're not supposed to use items, characters, etc. that have a copyright to them w/o the permission of the company.  That looks to me like it's a transfer perhaps they copied the design from a page with buttercream, let it get hard in the fridge, and then laid it on top of the cake and pressed down to transfer it.  They probably then went over the outline with blue tint buttercream by how it looks.

AThat cake looks like it was made by Don Buciak (http://www.flickr.com/photos/donbuciak/) He works in buttercream. Don't know that there is a name for his "technique".