Dark Souls - No Undead Burg, only an elevator straight to the cathedral, then you get a key to open the waterduct key near Firelink Shrine that leads to Capra Demon and then the rest of the game.
Bonus round - the butt dragons in Izalith respawn. Weapons have the same durability as in Dark Souls 2. Instead of Ornstein and Smough you fight two Ornsteins. In Anor Londo there are silver knights before and after that tower that blocks the path to the two archers. Instead of finding the Spider Shield in the Depths you find it at the bottom of blight town and enemies no longer drop dung pies. Leaving and reentering the game does not restart Bed of Chaos any more, you have to do the three phases in one go. Crystal caves don't have crystal drops showing you the path.
Bloodborne: all dodge animations and invulnerability frames are now DS style heavy rolls
(I was gonna go with the only ammunition is blood bullets but then again a lot of folks just brute forced without using the gun anyway)
Banjo-Kazooie: Every time you collect a jiggy you are booted back out the stage ala Super Mario 64, the note collectable system still stands as is
Castlevania Symphony of the Night and all its successors: No backdash
Oh man, just imagine, recurring canned dialogue related to the enemy type
Going through the catacombs conking out the reviving skeletons...
"No bones about it"
"No bones abo-"
"Spare ribs tonight"
"bone appe-no bones abo-bone appet..."
This concept could be a thread in itself, it's so wonderfully horrible
As it happens, we're currently working on heroic Mekkatorque, which as a guild that a good half of the members or so are unwilling to talk on mic due to either shyness, lack of confidence in their English skills or to simply not having the tech is making the fight... a challenge.
(The fight basically singles out three people at a time; each of them needs to press three buttons in sequence, but only the other people can see which buttons they are)