Infinite Rocket Launcher

In order to unlock the Infinite Rocket Launcher, you must beat the game, and then start a New Game Plus. When you meet The Merchant again, you can purchase the Infinite Rocket Launcher for 2,000,000 pesetas. However, you can get that price down to 1,600,000 pesetas if you have the Leon w/Rocket Launcher Charm.

End the village battle before Chainsaw Man appears.

Upon entering the village where the car driver is being set ablaze, you can go onto the roof in the house where you get the shotgun switch to any long range weapon (sniper rifle), Aland shoot the bell in the distance.

After doing so the cut scene that makes everyone leave the immediate vicinity will trigger immediately instead of after four minutes.

Egging Salazar

Salazar is allergic to eggs, so save up a couple of Golden Eggs to throw for his fight. One Golden Egg will cause 70% damage, and two will kill him instantly.

Kill Los Dos Gigantes Without Luis

During the fight with Los Dos Gigantes, Luis will retreat to find some explosives. If you manage to kill both Gigantes without Luis returning and using the explosives, he'll react with confusion. If you wait for Luis to return with the explosives, but kill both Gigantes without his help, he'll say a different line and react with disappointment.

Shoot The Lake

When you get to the lake before the Del Lago fight, head to the end of the dock and start shooting into the water. You'll be able to kill a few fish before Del Lago itself appears and triggers a unique game over.

Scoping The Body Bags

You'll reach a section where you have to maneuver through a room while carefully avoiding several hanging body bags. If you touch one that contains an enemy, it'll start attacking. However, this can be made much easier if you have the Biosensor Scope. You can use it to peek into body bags and see which ones contain enemies.

Ashley's Armor Effects

Ashley's armor is more than just another outfit. As long as she wears it, she's impervious to almost all attacks and friendly fire, including the Rocket Launcher. She'll shrug off getting hit by bullets, but still act disgusted if you throw eggs at her. She will also be too heavy for enemies to pick up, and Leon will have an extra animation where he holds his back in pain after lifting her. This armor makes several sections of the castle much easier to get through.

Brute Quick Kill

When you first fight a Brute, lure it to the nearby hanging bridge, and then throw a grenade at it. If positioned correctly, the Brute will stumble, fall off the bridge, and die instantly. It will even leave its loot on the bridge. This method will save you lots of time and ammo.

Méndez Quick Kill

If you have the Bolt Thrower that's been upgraded with Attachable Mines, you can kill Méndez very quickly. Go inside the building where the boss fight takes place, but be careful not to walk far enough to trigger the cutscene. Carefully shoot at least 4 mines on the ground where Méndez will spawn at the beginning of the fight. Then aim up at the central wooden beam going across the ceiling, and shoot at least another 6 mines on the beam. Then walk forward to trigger the cutscene. When the fight starts, Méndez will trigger the mines on the ground; if they don't kill his first form immediately, they will still severely damage and leave him wide open to your attacks. When Méndez starts using his second form, he'll grab on to the center beam on the ceiling and trigger that second set of mines. If done correctly, Méndez will die in a matter of seconds.

Armored El Gigante Quick Kill

When you fight the Armored El Gigante at the castle ramparts, you're supposed to go through the whole area while dodging its projectiles, and eventually kill it with a cannon. But if you have a Rocket Launcher, you skip all of that and kill it with a single hit.