-If you find your rifle is empty, you can also defeat the Regenerator by shooting a mine into the spot around the parasite. If it is on its back, simply shoot its legs with your handgun then fire a mine into its back. If this does not work, scout out where the parasite is on the Regenerator and try again.
-When low on ammo, shoot the Regenerator in the leg with a powerful gun to make it fall to the ground. Run up to it and slash it with the knife. Once you start attacking it, it will not be able to fight back or stand up. Keep attacking it until it dies. Note: Regenerators can attack you while they are on the ground, so you may get hit once. However, this technique saves much needed ammunition for the island and sewers. Make sure to have at least an Herb and be ready for an action command.