Hello there!
With over 230 hours (not including resets) into rejuvenation I can positively say that I'm in love with this game. Enough to where I'm considering doing a run-through again as a challenge run, which is where Monotype peaked my interest. However before I got into the run, I wanted to do some preparation as to what I was going to get into by going into the run, notably difficult fights, and how to possibly deal with them, so I don't spend 10 hours at my screen wondering "How do I even do this". I was CONSIDERING doing an Intense Mode run of this, though with given difficulty... I find it unlikely. I'll state what I think might be possibly problematic Fights.
Venam - Ghost monotype is limited to Very Very few early game pokemon. Before Venam, the only mons (if I recall correctly) that we get access to are our starter (dartrix by now), & shuppet... Seems like a major annoyance.
Marianette - What. A. Nightmare. With the field, and our ghost attacks no longer being able to do a single thing, and having pokemon like Bewear to worry about, this seems like one hell of a battle. And our team hasn't even improved! There's only one pokemon we could POSSIBLY add, and that's oricorio... of whom we don't get access to sensu form but for my Sanity's sake, i'll say it's legal. But that's still just a team of Dartrix, Multiple Shuppet (probably), and Oricorio. That... doesn't help.
Narcissa - Even though we are super effective against her and we recieved a MASSIVE team roster increase, she is super effective against us... And that sounds. Pretty bad.
Angie - This battle is always a nightmare, no matter what you're doing.
Then comes a middle ground of a lot of fights that I'm not sure how well I will fare against. I'm just overall, unsure.
Rift Gardevoir (?) - Not exactly sure how this battle pans out for a ghost monotype. Though this is very late game, so I wouldn't be surprised if we have checks nonetheless. Still seems like a nightmare... Literally.
If any of you have any comments/questions/ideas for this run, Do let me know! Whether that be possibly more difficult fights, theoretical solutions to battles, or just if you got something to speak your mind about. There are a lot of cool pokemon i plan on using over time, but I just hope that this doesn't make me pull my hair out when I eventually do start to do it...