Khezu

Use a fire weapon, I used the Barbaroi Blade (a great sword)

Don't attack too much at once, attack the head from the side when it spits electricity is a good time (with the GS you can even do a charge attack)

Take the time to learn it's attack patterns, you will soon find they are very predictable (he almost always does his body shock attack after a jump attack)

If he keeps killing you when he is in rage mode (he breaths smoke and when he does jump attack he is electrified) leave the area and let him cool down remember you have 50 mins so use it

Get the best gun and get on a ledge stay away from the edge of the ledge and gun it with crags and clusts etc.

The easyiest and fastest way is to bring the these items:
1 shock trap
2 trap tools
2 genprey fangs
10 potions
10 mega potions
Paintballs
Tranq. Bombs
And as many large barrel bombs, large barrel bombs+, and 3-4 small barrel bombs or small barrel bombs+.

First find it and use a paintball. Then try clear the area of monsters except bugs, lay a shock trap and lure it onto it. Now place as many lg. And lg.+ bombs and you can and one sm. Bomb then run!. It should do enough damage to make it run away. Find it again using the paintball/mini-map, once you find it you can do one of 2 things:

1: attack it with your weapon(i used long sword)but only do 1 attack then back off and repeat until it has ran away afew more times then lay another shock trap and use some tranq. Bombs on it to capture it.

2: lay a shock trap and lure it again onto it and use up your last lg. And lg.+ bombs and a sm. Bomb, it should run again(if not attack it afew times and it should run)once you find it again use your last shock trap after afew slashs and use some tranq. Bombs on it to capture it.

*NOTE* Use paintballs whenever you see it's mark on the map go out and I didn't list whetstones because I always kill it even before my long sword decreases.

HOPE THIS HELPS

The Hardest way can a man use to kill khezu is to use the kut ku stave with the ff, items:
50Powercoating
30Sleepcoating
3Large Barrel bomb
10Megapotion
10Potion
10Herb
10BLUEMUSHROOM

I used bone katana "shark." It bounces off of everything but the head and the legs, if you can get a good horizontal slash on them. But when you bounce off of it, it can throw you far enough away to dodge it's electrical attacks. If you hit the same leg, it will fall down and you can bash on it's head.