Literally: mountain-forest spirit – ghost / bewitch – mountain-water spirit – mountain-water spirit… probably.
Alternately: Various malevolent spirits (aka bakemono, 化け物, or mononoke, 物の怪) of the mountains and rivers, born of the “miasma” found in such places. By metaphorical extension, the phrase also describes a group of people who do bad things to serve their own greed.
Notes: These characters are all pretty rare; the only one even remotely close to common is 魅, which is included in the daily-use (常用) set literate adults are expected to know. In fact, it’s kind of hard to even pin down the “meanings” of the characters precisely without in-depth research, because apparently they (and this compound) go back thousands of years to ancient China. Again.
That said, while at a distance this yojijukugo may look like a mass of tiny lines, closer inspection reveals that each is based on the “demon” radical (鬼), wrapped around the left and bottom, and that the remaining component is often phonetic – so 魍 shares a pronunciation with 網, “net,” and 魅 with 未, often a prefix meaning “not yet.”