This is awesome. It not only pays tribute to the game, but it reminded me so much like an official poster for a probably 80's horror flick that might've came out from the period. xD The style of how they're drawn looks like the artist who did the illustration for Animal House, in a small sense.
Day Of The Tentacle is the sequel to Maniac Mansion, where Purple Tentacle drinks water from a polluted river, and turns evil and megalomaniacal. It's a fabulous game, which i thoroughly recommend you seek out and have a go at - you'll probably pick it up for dirt cheap on EBay, as it's been around for a long time.