Season 5 of Lucifer presents another obstacle to Lucifer's life and happiness: Michael, his twin brother. Michael is not the twin brother you would want around. He's the devil that Lucifer never was. Michael enjoys creating havoc, especially in Lucifer's life. He comes to L.A. to do just that, so much so that Amenadiel goes down to Hell to bring Lucifer back to sort out the mess.
While Michael revels in mucking up Lucifer's life, he also seems to enjoy doing the same for his brother, Amenadiel. He gets in their heads, manipulating them and those they care about in order to bring about his great plan. Michael lies (unlike Lucifer), but he also uses the truth to his benefit. His superpower is sensing and bringing up others' fears, and then magnifying them. He seems to play with our beloved characters and do horrible things to them.
Increases Linda's Fear of Motherhood
Linda has evolved throughout this show, and she's become someone that all seem to go to for advice. Yet, she also has a secret. She's worried about being the best mother for Charlie, her son with Amenadiel. Part of her fear is motivated by his half-angel status. Another reason for her fear is based on her past; she had a child once before when she was young, and she gave the baby up for adoption.
This weighs on her, even though she recognizes that it was the right decision for her and her child. Michael knows her secret, and he reveals it to her before she's ready to deal with it. However, Linda is a champ, and she does deal with it. She's a very special human as Amenadiel once had boasted, and luckily, she isn't as easily manipulated as others on this list (i.e. Dan).
Masquerades as Lucifer with Chloe
What is particularly dark about this one is that Michael decides to not just continue the ruse with Chloe, but to push it one step further by being romantic with her and potentially initiating sex. This is diabolical in two ways. First, it abuses the love that Chloe and Lucifer have for each other.
Chloe and Lucifer have built up this love over seasons, and they have yet to be fully romantic with each other. Second, it would be tricking Chloe to do something without her consent. Luckily, Chloe is smarter than Michael realizes, and she figures out the ruse before anything serious happens.
Blocks His Siblings' Access to Dear Dad/God
Lucifer learns from Amenadiel that Heaven is different now. None of the other siblings have access to dear Dad/God except Michael. While it's suggested that dear Dad/God isn't talking to Michael, Amenadiel does state that their father is listening to Michael. This proximity and influence to dear Dad/God could have terrible consequences for the rest of the children.
If Michael's story and opinion are the only ones dear Dad/God listens to, then his perspective will be narrowed. On top of this, it gives Michael too much power over his siblings. This is already on display when dear Dad/God actually comes down to earth to stop the fight between Michael, Amenadiel, and Lucifer. After all, Lucifer once killed another brother, and dear Dad/God didn't try to stop that.
Manipulates Dan At Charlotte's Grave
After being tricked by Michael to go back to the house where Amenadiel, Lucifer, and Charlie are, Dan sees Lucifer's devil face. He's terrified. Immediately, he goes to Charlotte's grave, asking for a sign. He's desperate to know what he should do, and suddenly Michael shows up in full angel attire to "guide" him.
As fans know, Dan loved Charlotte, and her death nearly broke him. So, seeing Michael take advantage of that love and desperation tells viewers a lot about his character.
Tells Dan to Kill Lucifer
Once again, Dan proves to be easy to manipulate. He's told that he needs to kill Lucifer in order to save others, so he readily does it, shooting Lucifer without hesitation. Lucifer had been with Chloe, and usually, Chloe would make him vulnerable. This means that Lucifer would have died by Dan's hand.
Strangely though, Lucifer is changing and is no longer vulnerable around Chloe. It seems Michael may have already guessed this and wanted Chloe to see it for herself in order to start to doubt her relationship with Lucifer.
Uses Charlie Like a Pawn
Amenadiel worries constantly about his son. At this point, he doesn't know the full extent of Charlie's powers or if Charlie even has powers. He's extremely fearful that something would happen to his son. This isn't helped because he has a reason to fear this, after all, both Remy (Heaven) and the wayward demons (Hell) tried to take Charlie.
One of the main reasons that Lucifer returned to Hell was to put the demons in order and to protect his nephew, Charlie. So when Charlie is sick, Amenadiel fears the worst. Luckily, it's just a standard cold, but this brings up another fear: Is Charlie human then? Lucifer suggests that Michael made Charlie sick, and judging by Michael's facial response, it seems that Lucifer was right.
Makes Amenadiel Spiral Out of Control
The reason why Michael used Charlie like a pawn was that he wanted Amenadiel to spiral out of control. Amenadiel has the power to slow down time, a power that he hasn't been able to evoke for awhile now. Fearing for the safety of Charlie, Amenadiel's power comes back, but stronger than ever.
He doesn't just slow down time, he stops it. Michael quips to Amenadiel, "I was hoping that you would spiral out of control. But completely stopping time - way to be an overachiever."
Turns Maze Against Lucifer
Maze may have had her problems with Lucifer, but she still worked with him - even protecting him at times. Michael uses the truth about her mother to manipulate Maze. She finds out that Lucifer has been keeping a secret - her mother (Lilith) is still alive. Lucifer made a promise to Lilith, and that is the reason that he didn't tell Maze. He also never told her Lilith's backstory.
Added to this, Maze wants a soul. Michael says that he can get her one, and Lucifer says that it isn't possible. Lucifer does tell the truth, but he also thinks he's above Maze since she's a demon. Michael takes advantage of this tension to turn Maze fully against Lucifer and to convince her to be on his side. In the fight in Season 5 Part 1, Maze protects Michael, rather than Lucifer.
Kidnaps Chloe And Makes Her Doubt Lucifer
At first, everyone thinks that Chloe was kidnapped by the murderer that they are investigating. It takes a moment, but Lucifer realizes that it was Michael who kidnapped her. Lucifer, Maze, and Dan rush to rescue her, but they didn't need to as Chloe was escaping.
Chloe was safe and unharmed, physically. Michael wanted to use the time with her to plant the seeds of doubt about Lucifer's love and her relationship with Lucifer. He suggests that Lucifer is now choosing not to be vulnerable around Chloe and that their love is one-sided because Lucifer has never told her that he loves her. It's sad to see Chloe doubting herself and Lucifer once again, and unfortunately, it's a familiar place for Chloe.
Suggests that He Manipulated Lucifer to Rebel
Michael tells Lucifer that he planted the idea of the rebellion on Lucifer - an action that got Lucifer kicked out of Heaven and made to lord over Hell. He also suggests that he planted the idea of coming to L.A. to Lucifer and abandoning Hell. Since Lucifer believes in free will and is extremely uncomfortable with any perceived manipulation, this doubt would be debilitating.
Lucifer may wonder if his choices were really his choices. He may start to wonder how long Michael has been influencing his life and decisions. This could cause him to fall into an existential crisis that not even Linda could guide him out of.