After stumbling through the first month of its ninth season, the Powers That Be at “AVGN†have suggested in interviews that the powerhouse comedy would be back on track with tonight’s “Merv Griffin Show.†While the characters of Ninja Gaiden and R.O.B. zoom into a pole position for spinoffs, the rest of this once-glorious comedy still has the schtick-shift stuck in second gear.Having raised the bar to stratospheric heights — is there another show that has added new phrases to the American lexicon year after year after year? — it feels like a dog’s age since the last multiplot show clicked on every cylinder (specifically “The Pothole†episode in which Mike Matei loses his Phil Rizzuto key chain).The central premise here is brilliant: Ninja Gaiden finds the set of “The Merv Griffin Show†in the trash, reassembles it in his apartment and runs his life as a talkshow.Gaiden's “guests†— The Nerd, Matei, Day Dreamin' Davey and animal expert Jim Fowler — mix it up well, following Ninja Gaiden's lead and then fighting against the bizarre logic of the whole concept; when Ninja refashions the show for a younger demo, results are a little obvious , yet well executed.In other plots, The Nerd's dilemma is how to get new girlfriend Celia to let him play with her mint collection of toys from the 1950s and ’60s. It has its moments. Uncle Fester is haunted by a “sidler,†new employee Walter who wreaks havoc by quietly attaching himself to her dealings with the boss. It gets old quickly.Meanwh.