I'm aware that the English version is slightly more difficult as there are more enemies in certain rooms (requiring different paths to run, etc etc). Does anyone have a list of ALL these differences? And perhaps a rough estimate of the additional time added to an optimal run of Leon A bc of said differences? Thanks in advance gang.

This is what I can remember off the top of my head. Nurmat ran the US version of RE2 for GCN Emu and has gotten pretty solid times on it. He's also done TAS videos for both the JP and US versions. The difference was a lot smaller than expected with only having a few secs separating the two. I'll just randomly guess with the time since I never properly measured how much time loss there was.

US/PAL

• Auto Aim is not present except on Control Type C for PS1? It has to be manually turned on in the menu on most versions. If you are playing the PC version you're stuck with no auto aim sadly. This applies to JP's arranged mode for PC as well.
• Zombies are much more aggressive and will generally shuffle towards players much quicker. Damage remains the same.
• Extra zombies at the beginning area of A scenario, 1 additional dog and licker in the basement.
• A few items are rearranged (mostly ammo) and there's more health present on the US/PAL versions.
• Most of the dodges done on JP work on the US version including the infamous Blue Hall "Yolo Horde",

A Scenario

• The main street area for A scenarios has two extra zombies at the beginning that are always near Kendo's Gunshop. The zombies are positioned differently, but it's not slower to run through compared to JP.
• Outside of the RPD gates has zombies arranged differently. Again not enough to impede movement since you use the same line you would on JP to get across.
• RPD Balcony has two extra zombies which slow these things down a bit. Depending on well you can move past these zombies you'll lose 3-6 secs of time here.
• There's an extra basement licker you have to deal with. It's not too bad to be honest if you know the proper movement. I'd say you lose about 1-4 secs doing the dodge.
• The crocodile can inflict 60 or 40 damage.
• In the Turntable Cabin the extra ammo placed inside is located inside the toilet instead of on the floor across from the key. This is actually a much better spot compared to JP.
• Final Birkin at the end has slightly less health. On JP it takes about 11 Magnum rounds to finish the fight. US/PAL only requires 10. 3 for the G3 form and 8 for G4 form. 1 sec time save.

B Scenario

• Mr. X is actually better on this version. He has a 50/50 chance of dealing two different damage values with either his right or left arm, you may receive less damage in return if you're lucky. His left does slightly less damage so you'll always want to tank the left arm if you can in most cases. Left arm can inflict 30 or 20 damage while right arm does 45 or 30 .
• Balcony here is much more worse and trying to get a no damage dodge is next to impossible as Claire. 2-6 sec time loss.
• Final Birkin has less HP. Would assume it's going to be 1 less shot than its JP counterpart if you're using GL or Magnum.

WOW @Roofress, this is so much knowledge to be had, thanks so much for taking time to relay all this to me! Essentially everything I wanted/needed to know, and then some! You're awesome!

About Mr.X. In US version his right arm punch deals 30 damage, left - 45. In JP right - 45, left - 30.