Sketchy/Picmonic are forms of the keyword method, where objects that sound like the words to be memorized are made to interact. Method of loci/memory palace involves associating items to be memorized with ordered stops in a location. I think of of method of loci as a series of keyword-type mnemonics, which is most useful for memorize lengthy ordered information (eg, a set of cards).
The underlying principle is elaborating the word to be memorized (something new, abstract, or otherwise meaningless) with a visual (something concrete, already understandable, or otherwise meaningful) and then establishing an association with other information by having the concrete visuals interact.