Although 'Mid-Life Chrysalis' was the first episode to take place mostly at the Venture Compound, 'Eeney, Meeney, Miney... Magic!' is the first to entirely unfold at such. Indeed, in the cold open we find Hank and Dean playing Ouija board in their pajamas. We are also more fully introduced to the differences between Hank and Dean.
After mistaking Doc's new renter, the necromancer Dr. Orpheus, for a 'Dracula,' Dean goes to wake up Doc to report this sighting, but Hank goes to Brock. Doc is disproportionately irate with Dean. Brock proceeds to let Hank hang out in his basement room while he does push- and pull-ups, and the resulting dialogue is where Brock breaks out of his mold from the first two episodes, shedding the twitchy-rage-machine and gag humor so dominating in 'Dia de Los Dangerous' and 'Careers in Science'.
Although this episode is the first to take entire place at the Venture Compound, it is not isolated from the outside world. To the contrary, we are introduced to Dr. Orpheus' daughter Triana, who, other than having a necromancer for a dad and affecting a goth fashion sense, is the first 'normal' person to appear on the show (to be explicit, she goes to public school and has a life outside of the compound). By comparison, previous episodes have only featured the 'normal' kind of people you would find in strip clubs ('Mid-Life Chrysalis') or Tijuana ('Dia de los Dangerous'), or have featured no ordinary people at all (i.e. astronauts Buzz Manstrong and Anna Baldavich in 'Careers in Science'). And they certainly have not featured anyone who could be conceived as a peer of Dean or Hank.
What's particularly fun about Triana Orpheus is that she can operate as a substitute for the audience by virtue of her normality – ergo her conversations with Dean are what it would be like if you or I talked to Dean. And what is revealed from those conversations is that the Venture brothers live a very isolated life, populated by a few adults and more than occasional violence.
Of course, based on the little we have previously seen in 'Careers in Science', Hank and Dean's experience is not that altogether different from their father's childhood and adolescence. The difference, it would appear, is Doc's self-loathing compared to his father's confidence and legendary status. The father-son relationship is not just replicated between Doc and the boys but actually exacerbated. Dean's head-over-heels crush on Triana should come as little surprise, given its allure as escape pod from the drudgery of his otherwise lonely and violent existence.
See also:"Dia de los Dangerous" (The Venture Bros. - Season 1, Episode 1) "Careers in Science" (The Venture Bros. - Season 1, Episode 2)"Mid-Life Chrysalis" (Venture Bros. - Season 1, Episode 3)