wait, What Time is it? - maxed the Consecutive Match Bonus in Versus Multiplayer - To do this, you need to reach the 10x match bonus by playing 11 games in versus. It appears that as long as you don't quit to dashboard or turn the console off, you can keep your bonus, even if you switch modes though there may be a timer that cancels it. you can get this by playing 9 matches (maybe 10, but it's not consistent) offline, in a private match with another controller and then playing the last few matches online in Versus. You won't see the bonus appear offline though so you need to make sure you keep count.
Welcome to the Big Leagues - Your skill and experience means you're ready for Standard Versus Multiplayer - to unlock this, you simply need to be locked out of the "casual" Versus section. To do this, you either need to have played Gears 1 and/or 2 or have played a few matches of Versus in Gears 3. Once the game deems that you have played enough that you no longer belong in the casual category, you will get this achievement.
Welcome to Versus - killed 10 enemies in Team Deathmatch - This is as it says. It can be done offline but you must have a second controller in.
The Versus Sampler Platter - complete a match of each of the six launch gametypes, Team Deathmatch, Warzone, execution, King of the Hill, Capture the Leader, and Wingman. You can do this in private matches as long as you have a second controller in.
Lambency - this is a viral achievement that requires you to Execute someone in multiplayer who already has this achievement. You can try and find someone who has it and see if they'll let you do this or you can just play online. Roughly 3/4 of all players have this achievement (including people who don't play online) so you shouldn't have much trouble getting it.
Welcome to Horde Mode - survive the first 10 waves of Horde - You simply need to make it from round 1 to the end of round 10 (which is a boss wave). Most online games will last this long with ease. For more information, see the Horde 2.0 section.
Enriched and Fortified - survive all 50 waves of Horde - This is far harder than Welcome to Horde Mode. it is definitely best if you find people to do this with and set out as a group to do it rather than try and play with strangers online. You DO NOT have to do this in one sitting but if you do, you benefit from having made cash to use on later waves. It can take 4-5 hours to do it in one sitting (during which strangers will usually quit). In later rounds, unless you have a lot of money, i recommend using Chainsaws and Bayonets to conserve ammo and use your money for revives. See the Horde 2.0 section for more information.
Welcome to Beast Mode - complete the first 12 waves of Beast - To do this, you simply need to finish a complete game of Horde mode (though the wording hints that they may add more waves in DLC) which shouldn't take longer than 20 minutes provided people don't quit out. See the Beast section for more information.
Wreaking Locust Vengence - get a Kill with each monster type on Beast Mode - You can do this by playing a private match with one other player. After you complete the first wave, you can kill everything except one human to gain all the points and money but if you fail the wave, you can restart the wave. If you can get to wave 3, you can kill most of the humans pretty easily and level up quickly so that you have access to all the locust. Once you've done this, just get a kill with each type of locust. This information is tracked in Stats --> Summary --> Beast.
Welcome to Arcade Mode - complete 5 Arcade Campaign chapters in co-op - You can get this quickly by playing arcade mode online or you can connect a second controller and just play act I: Chapter 1 over and over until you get this.
