Like many of WandaVision's central characters, Señor Scratchy took a backseat in the series finale. Director Matt Shakman, however, revealed in an interview with Entertainment Weekly that a scene cut from Episode 9 did the exact opposite. It depicted the MCU's Señor Scratchy transforming into a giant demon to protect the Darkhold from Monica (Teyonah Parris) and Darcy (Kat Dennings). Unfortunately, the sequence got cut, and audiences never got to see the seemingly harmless rabbit trample around in Goonie-esque style.
Señor Scratchy has left fans with lots of questions, like which Marvel Comics' character it was. A popular theory circulating online is the rabbit was the adaptation of Agatha's cat, Ebony, which could be true. Although, it's worth mentioning that Agatha has aligned herself with several supernatural characters in the past. And since Harkness has lived for so long, she's probably recruited a demon or two along the way.
Agatha's Grandchildren
As far as which of her allies it can be—our money is on one of Agatha's grandchildren. The demons, Thornn, Brutacus, Hydron, all hold the ability to transform into beastly creatures, and any of the three could be little old Scratchy. Though out of all her grandchildren, it's likely Brutacus. He transforms into a leonine beast in the comics and based on how Shakman described the monstrous Scratchy, the two sound very alike.
The fascinating thing is that even if the demon inhabiting Scratchy doesn't turn out to be one of Agatha's grandchildren, he may still have a future in the MCU. Señor Scratchy didn't die in the finale, and more importantly, Wanda was unaware that a demon inhabited the rabbit. As such, it probably got left behind in Agatha's home.
Agatha's rabbit is still pertinent here because the demon inside might have the power to counter Wanda's brainwashing. Assuming it is a demon with consciousness and magical powers, Señor Scratchy could be the key to giving Agatha her personality back. Of course, there's another reason having Scratchy or someone else wake Harkness up fits into the ongoing plot.
Agatha Harkness In 'Doctor Strange 2'
After Wanda brought Agatha down in the finale, the old witch tried to weasel her way out of the situation. She claimed that the Scarlet Witch would need her help to control her new powers, which Wanda responded to by saying she knows where Agatha will be in that scenario. Wanda's response was probably just a witty one-liner, but it potentially has implications for the future.
Considering the predicament Stephen Strange (Benedict Cumberbatch) will be in, in Doctor Strange in the Multiverse of Madness, Agatha could resurface. Strange has the task of reining Wanda in ahead of him, but he's at a clear disadvantage. The Scarlet Witch is poring into the Darkhold, presumably harnessing its power.
The Sorcerer Supreme won't be able to counter the book's dark magic without seeing it himself, which is why he'll probably need Agatha's help. She's read the book herself, making her a handy ally to have around. Then again, Wong (Benedict Wong) seemed to have just as much knowledge of magical tomes, so perhaps he can offer Strange the information he needs, eliminating the need for Agatha's return.
Whatever happens, Señor Scratchy is still roaming around the MCU. No one can say what the little critter will do now, but a demon wandering about is bound to get into more evil and mayhem, eventually. It's just a question of when.