a helping hand - 5GP: swap an allies weapon for a Rocket Launcher, Fuel Rod Gun, Sniper Rifle, Beam Rifle or Brute Shot
skewer stopper - 10GP: end a players sword spree
pest control - 5GP: kill 5 drones within 10 seconds of each other
[Edited on 02.06.2012 3:10 PM PST]
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Here's mine (some have hints of possible future videos from me): Thunderstorm - 10GP - Get the Thunderstorm skull starting from the armory room checkpoint without killing any enemies or perma camo glitch Sorry Sarge - 25GP - Bring Sarge to the end of Cairo Station on Legendary It Came From Above - 25GP - With Thunderstorm on and no permanent camouflage glitch, assassinate 10 Ultra Elites on Cairo Station, Legendary difficulty without dying But That's Impossible! - 50GP - Clear the bomb room on Cairo Station in less than 2 minutes, Legendary Solo all skulls on Rise My Brothers! - 25GP - Rescue all marine prisoners on Gravemind, Legendary difficulty, and bring them to the Mausoleum fight without dying None Will Be Left Behind - 10GP - Bring all possible Elites (including the 2 Spec Ops Elites that come when the 2 Grunts are killed) on Uprising to the end of the level Pacifist - 25GP - Complete Uprising on Legendary without killing any enemies and without meeting opposition (for most of the level) Calling All Hunters - 10GP - Get 4 Hunters to the Scarab boarding platform on Great Journey One Final Effort - 100GP - Bring 4 Hunters and Rtas Vadam to the Tartarus boss fight and get 6 Johnsons (or 3 or 4 if there's a limited supply)