If the target permanent is an illegal target by the time Maelstrom Pulse tries to resolve, the spell won't resolve
If the target permanent is made up of multiple cards (due to mutate or meld, for example), that permanent's controller puts all of them on the top or all of them on the bottom
The spoilers have already got some cards moving, but generally, there is a lag time as players figure out what cards they want before they spike
You can always sacrifice Grinding Station to itself if need be and there are a number of cards that could be used depending on colours and number of artifacts you can bring into play and sacrifice
Underworld Hermit can also lead to some compelling situations, perhaps not even in just Squirrel decks
If you do, create a 3/2 colorless Eldrazi Horror creature token