General Idea: Sit back, make friends among everyone when possible, help people out however they need, until there's one person left other than you. Then brutally backstab him or her. 
On second thought, if the last player is a 'her', let her win and take her out to dinner 
The deck is a bit oversized, but its definitely a multiplayer deck, so this could be a plus.
Note that you'll rarely keep EVERYONE happy with this deck, but you never can anyway, so its not a problem, really.

Card by Card
Creatures
1x Questing Pheldagriff: Helps people out with a variety of effects - he is also a win condition in disguise.
3x Guiding Spirit: Help someone out and get them back a recently dead creature.
2x Iridescent Angel: One of two prime win conditions - either play it after everyone else is out, or claim that its only for your defense.
2x Phantom Nishoba: See Iridescent Angel
Spells
Fiery Justice: Once again a prime multiplayer card, its also very nice from a diplomatic standpoint.
Energy Bolt: Help a player out with some life. Can also deliver the kill when necessary.
Captain's Maneuver: Help a player out by reflecting a spell to another source - if you REALLY want to be diplomatic and can afford the life, send it to yourself.
Terminate: This won't make the controller happy, but it could make a friend for you with a player who was powerful but got himself in a jam.
Elemental Augury: When you're playing Mr. Nice Guy, it is used to favorably stack your "allies" draw. Later, it does the same in a negative fashion.
Hero's Reunion: You gain 7, or another player gains 7. Good diplomatic card.
Gerrard's Command: Lend a player a beefed up surprise blocker...the attacker probably won't like it though.