On first watch, "The Cursed Cabinet of Professor Mads Markson" impressed me a good deal. Sure, it is quite strange and it wasn't perfect, but did love its spookiness, the fun and how much Penn and Teller have grown on me (great as an act, Penn's very loud vocal delivery just took some getting used to). How successful any episode of 'Scooby Doo and Guess Who' is is dependent on how the guest star fares, if the guest star(s) is/are good, that's already the makings of an episode worth watching.
"The Cursed Cabinet of Professor Mads Markson" certainly is an episode worth watching and makes good use of Penn and Teller. While not one of the best episodes of 'Scooby Doo and Guess Who' (which has actually really impressed me on the whole, despite not every episode working), it is one of the better faring episodes up to this early stage ("Elementary My Dear Shaggy" being the best though easily) and has one of the stronger faring mysteries on the whole.
Sure it's not perfect. Penn doesn't immediately settle and seemed ill at ease initially, which is unlike him actually. You'd certainly expect a comment like "ghosts aren't real" to have a lot more oomph with a voice like Penn's, but he seemed unusually self-conscious.
Did feel too that the fart joke was incredibly stupid and really out of place, not just in this episode tonally but it really sticks out like a sore thumb when thinking about the jokes throughout the whole show in a not so good way. It is on the strange side sometimes too and some of the character animation seemed very uninspired and lazy.
However, there is a lot that is good. Absolutely loved the spooky location and the atmosphere was also suitably eerie. The villain is suitably creepy, especially how he looks. Penn and Teller on the whole are strong guest stars and put to good use, not being anonymous or underused but also not dominating. When Penn relaxes, he is good fun and really liked his interaction with the gang.
Who are all on great form, though Velma's summations are still too out of the blue. Shaggy and Scooby are their usual funny and loveable selves, love their chemistry, and it is really great to see more of Daphne's truly refreshing quirkiness (have really been quite struck in a good way by how much Daphne came on as a character since the beginning of the franchise). This is one of the few reveals of 'Scooby Doo and Guess Who' too where the perpetrator and overall reveal were a big shock, not expected at all. Love the magic/illusion tricks too, nice to make good use of Penn and Teller's occupation.
The animation has a lot of atmosphere, rich colour and even richer attention to detail. The music is dynamic and groovy, also loved the modern spin on the iconic classic theme tune for 'Scooby Doo Where are You', although it is too short. The writing is fun and smart. A vast majority of the voice acting is very good, with Matthew Lillard nailing it as Shaggy.
Overall, liked it a good deal though it's not perfect. 7/10.