Here is some tips for beating legendary:

@FriedMetroid

Drones are weak against explosions. Use grenades, rockets, brute shots, needlers, anything that makes explosions. GBP skull does wonders here. Sputnik is awesome as well.

The Jackel Snipers and normal Jackels have been seriously upgraded during the last few difficulties. The normal Jackels fire charged shots more often then ever, and their fire rate is increased a lot. Snipers have DEADLY accuarcy, be careful, otherwise you could be in a "BOOM HEADSHOT!!!" moment. my advice is to hide behind walls, and when you see them not looking at you...Give them a headshot they deserve so much. For the normal jackels, sputnik and gbp skulls do wonders. <--- aplpiles to snipers also.

@KIWIDOGGIE

If you mean the Flood, or the Spec Ops Elites wielding swords, then I have some tips for them as well.

The Ultimate flood weapon, is the energy sword, it kills them in one hit. Also, it only uses 3 ammo, because they are just dead already....

Always active camo when you have the chance, it helps....but not for long. Thats when you strike them with the sword. If they still melee behind your back, make sure you turn around a lot, to get the idea where the enemy is coming from.

The Ultra Elites, now here is a tough opponent (except the flood juggernaut, but that has to be modded to fight it)
On legendary, these bastards come in BIG NUMBERS (not so much in the beginning, but later on they will appear often. They have these qualitys:

Fast Fire Rate
High Health
High Sheilds
Second weapon
Anger Management Problems

They have a range of weapon choice, ranging through needlers to a beam rifle. Their second weapon is ALWAYS a energy sword. Two things make them switch to this weapon

1. You walk too close to them, and they get pissed.
2. They see you wielding their sacred blade, and they think: "OmG tEh n00b oVa TeHiR iS wIeLdInG MeH bLaDe!1!11 I mUsT kIlL TaHt N00b! (that took longer than you think to type out) Anyway, they get pissed, and switch to their sword.

If you still have questions, go to GAMEFAQS.com for a GUIDE for HALO 2 for BEATING LEGENDARY! And no, I am not advertising. Just a little guide that should help you if you still have problems with beating legendary.

Good luck!