The beginning battle scene, both for the characters involved and the animators.
When a building collapses because of an earthquake, Maou manages to place magical barriers around every single person in the restaurant at once. Considering magic power for demons comes from fear, the logical explanation is that he used the fear the people in the restaurant felt to protect them.
Lucifer/Olba vs Alsiel/Emi. The explosions literally cover the entire sky. Lucifer Beam Spamming, Emi calls her holy weapon, Olba shoots off thunder bolts, and Alsiel hurls cars like baseballs.
You'll notice that Maou was not in the above line-up. This is because after he finishes stopping time, gently putting down the entire highway bridge and protecting the civilians, he ends the fight almost instantly. He crushes Olba with a glare (that somehow sends the priest through the wall), and Flash Steps right in front of Lucifer's face. Maou then creates a chain of magic circles miles long to deliver a Megaton Punch that could be seen from space.
Lucifer's face when Maou teleports into his face is priceless. He practically wets himself.
Chiho is not afraid to unleash the F***ing Fury on Maou if he should bring up any talk about whether she wants her memory of him erased for her own good... or if he doesn't take handmade double decker lunchboxes from other girls seriously. Demon lord and ability to level city blocks by will be damned, she will launch across the table, bodily drag you to her end and shake you silly till you answer her properly.
To be fair, Maou had told her shortly before that he was currently out of magic, so it's not like could have done much about it. Whether or not she remembered that at the time is another question.
Let's not ignore the extent of Maou's, Alciel's and Emi's achievements concerning their dedicated and sincere efforts in the mundane world and their work life.
In episode 12, just when it seems that Lucifer is going to become The Starscream again by conspiring with Olba, he reveals that he has tricked Olba into calling the Moon down to Earth ostensibly for the benefit of Archangel Sariel where in fact the fear and panic generated by that phenomenon provides Maou with much more power instead. He then knocks out Olba and declares that "Heaven is a place on Earth, in a six tatami-size apartment". Then adds that "Being abumis the best".
Following that was a sequence that put Episode 5 to shame, where Maou wrecked Sariel.
And then Sariel tries to take Chi as hostage. SHE UPPERCUTS AND KICKS HIM INTO THE NEXT BUILDING. Actually, Maou used a disguise to trick Sariel. The lesson here: Don't try to use underhanded methods in a fight with an Evil Overlord as opponent. You will lose!
Right after Maou gets his power back, it takes the form of a tornado of energy.
Maou rallies the MgRonald's staff in episode 9 to get customers in by using bamboo trees and decorations to attract customers.
In episode 10, when the alligators escape the cage and make their way into the pool, the panicked swimmers knock Chiho down and Emi kneels to help her. Maou leaves the MgRonald's and walks toward the pool, gathering magic force from the frightened crowd as he goes. The music gets awesome, he gathers a black cloud of force around him, and Emi and Suzuno look on in fear, and Chiho in awe. The gators duly line up before their master.
In Volume 6, Chiho's absolutely insane plan of willingly getting herself kidnapped by Farfarello and Erone against everyone else' plans, just so that she can talk to him and try to get him to leave peacefully. Her subsequent speech shocked both him and her friends (who she was unintentionally broadcasting speech to via Idea Links), before Maou came in and finished the job. Emi, Suzuno and Maou goes beet red due to embarrassment, and even Suzuno said she might start worshiping Chiho now.
Also, even if it's unintentional, Chino somehow managed to broadcast said speech via Idea Link to multiple recipients, for multiple minutes, shocking Suzuno since that spell was way more complex than single target version, which Chiho only managed to do so for just a few seconds merely a day before.
Volume 10 has Alciel successfully communicate with Emilia to stage a fight and play Olba and the angels for fools using a single sentence on a letter.
