There are Dark Souls 3 mods that dilute its difficulty (opens in new tab). And then there are Dark Souls 3 mods like TKGP's Enemy Onslaught. Which essentially turns Lothric into a Royal Rumble-style free for all. Yeah, good luck with that.
Enemy Onslaught does this by duplicating enemies—both run of the mill baddies and end-of-zone bosses—and by removing the event IDs of clones. In turn, this lets reproduced bosses leave their designated arenas (something standard bosses cannot do), and also allows swarms of friendly NPC summons to lend a hand.
In the interest of balance/not having YOU DIED etched permanently into your brain, I reckon the latter sounds important. Here's some screens:
"This mod duplicates every enemy in the game, including bosses," explains TKGP's Nexus Mods description (opens in new tab). "Nearby enemies no longer prevent you from sitting at bonfires because some would be basically unusable otherwise. Any time you enter an area you'll get a smattering of souls from unfortunate clones falling off the map; enjoy it, because you'll need the help.
"Most of the game is very hard but still doable on 3x enemies, but some bosses are practically impossible on your own. Even on 2x you will have an extremely difficult time in a couple places. Please don't be shy about switching the difficulty if you get stuck.
"You may also notice a vanilla mechanic that usually doesn't come into play very much: most enemies will calmly stay out of the way if you're already being attacked by a few others. If you find that a little underwhelming, the 'Impolite Enemies' optional file will remove their qualms about ganging up on you."
TKGP says that to the best of their knowledge Enemy Onslaught can be used online without issue, but that they recommend switching to offline mode "just to be safe"—particularly if you don't play with friends. TKGP also notes that using the aforementioned Impolite Enemies add-on will "absolutely" lead to a ban, so best avoiding that one.
More information on Enemy Onslaught, including installation instructions, can be found here (opens in new tab).