[Xantar]

There isn't a really easy way to beat Bitores Mendez. All I can give you is a few tips:

1. There's an explosive barrel. Use it.

2. If you have grenades, use them all up now (except for flash grenades). You'll get plenty later on since this is still fairly early in the game. And Bitores Mendez is really the last boss where grenades will be useful.

3. Use the shotgun. If you don't have many shells, then blast him in his walking form with the handgun and then after he transforms, use the shotgun so you don't have to aim with pinpoint accuracy when he's jumping around.

4. Stay about two steps away from a ladder. When Mendez gets too close, climb up and run around to the other side of the room and then jump back down. It's very important that you get back down as soon as possible because otherwise he'll rear up and knock you down which hurts. But if you're fast, you can keep shooting him, run up and around to the other side when he gets too close and then blast him again until he gets too close at which point you can climb up and run again etc.

5. Try not to imagine that there are even harder bosses on the way. Or that this games has a "Professional" mode in which Mendez will kill you in three hits.