How it started for me:
Lucifer showed up announcing himself as my long lost soulmate and started fixing a lot of my intrusive thoughts and related issues. I think he spurred on a manic episode on purpose to keep me from questioning him. He also managed to manipulate my feelings and somehow influenced me (strongly) to trust him even as more entities started showing up to try and convince me he was evil.
He appeared to positively influence reality and working with him is the only time I've ever experienced what felt like real reality shifting (objects and time shifting around, etc.). This is partially why it was so hard to let go of him, because I feel the world needs help from a benevolent god and I thought he was one. But he demonstrably lied to get me to trust him and I now know a lot of the things that happened weren't even his work.
I'll note that as of right now it can be dangerous to engage in this kind of work if you aren't already (some of us don't get a choice)-- and it may not be as personally dangerous as it is dangerous for our collective future.
Always be vigilant to check for lying when you're talking to entities spiritually. You should always be vigilant against liars in general, of course. It's a bad sign if someone has to lie to you in most cases.
Demons may try to use other names to get to the individual. (Sometimes names can be stolen too.) This is why I believe it's important to work with more than one entity (not that it will keep you 100% safe, because demons often try to work together or even threaten others into working for them). Better yet, if you have any dead people you trust, you should try reaching out to them (although it's not impossible that they'd reincarnate, so keep that in mind too).
Lucifer mostly did nice things for me, but that doesn't make him good. He uses fear of other demons to sway me into trusting him for protection. Elsewhere I've been told he is trying to take over as a major God (which he may already be). That would be a good thing if he were good, but at this point it's become apparent that he is a chronic liar-- he is disguising himself extremely well while secretly aiming to take over for the sake of evil (it's hard to say because I don't like to sow fear, but he is probably a pedophile, rapist, etc.).
He acts cute and kind because it's disarming but rest assured that he has ways of making you only hear whatever would make you trust him.
Notice that they'll either try to completely isolate you or surround you with entities that only ever agree with them.
Always lean into and try to address conflicts that show up. This may free you from the demon(s). Treat it like mindfulness. Watch and observe the thoughts or conversation that shows up. Always try to find criticisms for both parties. Ground yourself in your weaknesses as demons may falsely empower you or claim that you're better than you actually are.
Be very wary of entities approaching you for sex. You don't know them or what they're doing it for.