Resident Evil 4 Remake adds a whole bunch of new mechanics to bring the original into the modern day. One of these is the ability to parry, and it proved so popular with fans that one modder, qingsheng, has retroactively added it to the original Resi4.
Parrying in the remake lets you deflect enemy attacks to stun them. Time it right and you can create an opening to get away, reload, or get a few hits in yourself. Parrying even cuts off regenerator limbs. It's a huge part of Resi4 Remake's gameplay loop, as you're constantly synergising the parry mechanic with your normal attacks to clear groups. If you don't, you'll end up being punched around like Redfield's favourite boulder.
Going back to the original Resident Evil 4 after getting so used to parrying can be disorienting given how fluid it makes combat. Enemies get too close or throw projectiles and you're forced to retreat or unload, which is ultimately more difficult. Getting good at parrying in the remake ensures that you always have a way to hold off enemies, even if you're running low on supplies. That's why the mod exists, and you can see it in action below thanks to a modder called Link.
To recreate the parry animation from Resident Evil 4 Remake, it appears as though qingsheng has utilised Krauser's slash animation. In the clip, we can see Leon swing to knock projectiles out of the air with Krauser's signature move. It's a little clunkier than the remake's mechanic, but given that the original Resident Evil 4 came out in 2005, it's an impressive addition.
The trainer comes with a whole host of other features if parrying isn't enough. One of the other major additions is being able to move around in cutscenes, while there's also finally an option to play Ashley without just replacing Leon. There are also a few neat quality-of-life and accessibility changes, like being able to press 'c' to bring Ashley close to you, auto-completing QTEs, and modifying the colours of the laser sight. You can also swap Luis for Ashley if you want.
If you're worried about the trainer being filled with malware, as one commenter pointed out that they got "tons of virus results" after scanning it, Link reassures that "it seems to be fine" and that "Most trainers are false positively flagged due to them making real-time edits to the executables that they require. It's nothing new".