Taking down Mr. X (standard)
When facing Mr. X in his normal form, you have the option of taking him down or running through the nearest door away from him. However, it's a better idea to take him down each time you encounter him.
I find the best weapons to take him down are the Sub-Machine Gun and the Gatling Gun. As they keep unloading the lead into Mr. X, it prevents him from getting too close to you before he passes out. You can then reap the rewards.
Taking him down will give you access to some ammo if you examine his unconscious body. At one point the result is unfortunately some Handgun Bullets (which is not exactly bad, but there are better rewards out there), but most of the time you'll receive ammo for the Shotgun, Bowgun, Grenade Launcher or Mangum (depending on which character you're using and at what occasion).
Other weapons that are good at taking Mr. X down are the Shotgun (regular and custom), Grenade Launcher with any kinds of Rounds, the Bowgun and the Magnum. The Custom Handgun is a decent last resort.
Added by: Volke Apr 22nd 2009, ID#6360