just yesterday /tg/ had a thread how a dragon or dungeon magazine wouldn't be feasible today anymore
I only know those magazines by reputation.
I know the general consensus is that printed media is dead, but I'm not so sure. My uncle reads geek magazines and comic books, my parents enjoy puzzle books, and my local newsagent still has a shelf of magazines ranging from kids stuff (a lot of lego magazines), gossip, and hobbies (gardening, cycling, and of course this DnD magazine).
On further reading, I'm not sure Dragon magazine is the niche this is going to fill. The main book is 28 pages with 8 of that being dedicated to the adventure, the rest being basic rules stuff. If they keep this format, it could be years of magazines until they reprint the entire PHB and DMG, and that's before you get to supplementary material like the Ghost of Saltmarsh boat rules. If that's the road they go down then I'm out. Even if they stick with just the basics that's still a few issues of content.
I think going for the beginner rout might be a mistake, and it might have better as an enthusiast magazine, but I don't know.
I did read the adventure thoroughly. It's interesting. There's a grave under the inn with a magic sword. A illathid creates some cranium rats to go in and get it. The game starts when the PCs go into the inn and find the place trashed. They fight a bunch of rat swarms before either heading upstairs and finding a cranium rat king interrogating people, or downstairs and finding rats digging in the basement. Once the cranium rats are defeated, the owner lets the PCs have the magic sword and the adventure ends.
It's not bad as far as a simple adventure goes.
Any advice on how to make an overpowered character as the bbeg but the player characters get their shit beat in the final battle but win through the power of friendship or god?
Sods law predicts players will score lucky crits, hit him with conditions, or worse.
So my advice would be abilities. Give him immunity to mundane damage, insane health regeneration, or something that can only be defeated with friendship. If you're playing 5e, legendary resistance is your friend.
Also, to get action economy, have him take more turns. Maybe one turn per PC, or one turn per other PC. Failing that, abilities like extra attacks can help.
I don't know what you have for a story, but I'd add a reason to leave the PCs alive. Like maybe his plan involves turning people into thralls or something. That way the players won't find it heavy handed when during the final arse kicking he doesn't deal the killing blow when a player is down.