The Walpurgisnacht is the strongest of all witch enemies from the Madoka Magica collab. This is because her falling building attack can destroy virtually all cats in one hit (except a few Uber Rares) due to its high damage being multiplied by her unfailing critical hits. Her area of effect is tremendously wide as well. Also keep in mind that this is one of few enemy units that looks like it is floating even though it is not (same case with other witch enemies and CyberFace).
Surprisingly, this enemy becomes very easy to beat if you have unlocked both Chibi Madoka and Chibi Homura and use them in battle. The Cat Combo called Best Friends involving these cats will further improve their “strong” effect against witch enemies (like Walpurgisnacht) by a massive factor.
Also, you can use any of the Uber Rares from this collab (Madoka, Homura, Sayaka, Kyoko, and Mami) since they have the same special abilities.
Without the chibis or normal girls, the battle becomes almost impossible to win. Other cats will instantly die in the process and not be able to deal significant damage before the end of the Walpurgisnacht’s attack.
This should not take long to do if you have Chibi Madoka and Chibi Homura. Just send out the two to eliminate the Walpurgisnacht. Do not worry about the Walpurgisnacht slowing them down in the process; she will not kill them easily, for their “strong” abilities and the activated Cat Combo will ensure that. Then, you can send out whatever other cats you want to finish the job.
If you do not have any of the chibis or the normal girls, then you will need the cats to stall the Walpurgisnacht enough so that she cannot approach your base. You will have to stall her for a very long time until she dies, so bring along Manic Lion Cat, Maglev Cat, and Awakened Bahamut Cat. These cats are fast enough to reach the enemy before she can stop them. For the course of the battle, always be sending out Manic Lion. Timing is critical here, so be sure to spawn him so that he is just outside the enemy unit’s attack area after she attacks. That way, she will hardly have to move or not move at all, and Manic Lion can deal as much damage to her as possible. At the same time, use Maglev and Bahamut to speed up your efforts. Just time the spawns correctly.