GAR0 has posted a little guide to NiWiFi play for Metroid Prime Hunters in the Nintendo forums. Here's a taste, hit the link for the full-on guide.

NOXUS
Description- An ice themed hunter with strengths to match.

How to use: Get your special gun and charge it. Get in close to an enemy and release it. Then fire at the head for better damage OR if you're quick, switch guns and hit in the head with that. Keep an eye on your ammunition. Your ammo runs out quickly if you freeze your opponents often. The regular shot of your special gun bounces off of walls, so if it misses on the first shot, you still have a chance to hit an opponent with that shot.
How to beat: Stand clear when you hear he's charged, and don't get in to close because if he freezes you, anyone with a powerful gun will come in and headshot you for a kill. You avoid his freeze by jumping and running, and you should be all right. Use your guns against him, his is slow.

ALT-FORM: VHOSCYTHE

How to use: Hold L when and watch the blade get bigger and more deadly. Hit your foes with it whenever you can, but it takes a second to reach full power. Use when you want ammo or escaping headshots. This is also good for people with slow guns if you can get in close.
How to beat: Get to higher ground, then hit him hard. He can't hurt you severely and quickly, but it does damage if he hits you. Jump and get to a ledge. He will switch to BIPED when he realizes he can't hurt you anymore, then hit him with everything you have.

UNIVERSAL TIPS REGARDLESS OF CHARACTER
Remember to keep your health up, always try to have it over about 80 unless you're about to kill and you're not taking much damage.

Get your special weapon whenever you can. It's the black orbs that beep when you get it.

To switch your third weapon, press the upper right part of the touch screen and drag thumb to the icon of your choice. Top icon is your character's special gun.
Find the character you're best with and excell with him/her.

When shooting, don't aim AT your foe unless that human is weak in the upper story and standing still. Account for the time it takes the weapon's attack to reach your opponent.

Metroid Prime Hunters Guide [Forums]