You do not need to have participated in the beta or be Lv100 in Gears 2 to earn this achievement.
In total there are 65 onyx medals you need to earn in order to unlock the Seriously 3.0 achievement, you will also need to rank up to LV100 but that will most likely come naturally while going for the onyx medals (When I hit LV100 I had 14 onyx medals.). The medals have tiers, kind of like challenges in Halo: Reach, it goes bronze > silver > gold > onyx.
Keep track of your progress easier with the help of Ctr Alt Defeats excel spreadsheet: http://www.xbox360achievements.org/f...d.php?t=333803
The information about every medal will look something like this:
NAME OF THE MEDAL
DESCRIPTION ( BRONZE / SILVER / GOLD / ONYX )
Every versus medal can be earned in private matches with custom settings VS casual bots or friends, I recommend you to set the number of bots to "Fill" if you're going to play the matches otherwise you will not be able to earn any of the important ribbons.
However, if you are afk playing, it helps to put the bots at 1 or 2 cause you will still earn progress to most of the medals.
Also remember that you can choose what weapons will spawn on what place, if you're going for fire kills for example, set everything to hammer of dawns or scorchers.
A nemesis is an enemy who killed you 5 times in a row without you killing him in the same match.
I don't have a super good method for this, I have been using 2 controllers and killed myself with the 2nd controller 5 times then executed the 2nd controller.
) enemies with a captive.
Press X while standing next to a downed enemy to take them as captive, you can only use melee and your pistol like this. You can knock out a great deal of these while going for leader captures.
Play in (5/10/20/30
) Gears events.
The way to earn it is to play online during 30 different Gears Events, to check what events are comming up, go to the "Event Calendar" option in the main menu.
) MVP ribbons.
You get the MVP ribbon by finishing a match with the most points. If you plan on playing vs bots, this will come way way way before you finish the 18,000 matches you need to play. Must be done with bots set to "Fill" or in a match full of players.
Reach Level (25/50/75/100
You gain EXP from pretty much everything in Gears 3. You get the most points out of playing Ranked Matches, however expect your opponents to be more skilled than in quick match. If you don't turn off your console you never lose your consecutive bonus either. If you want a good method to gain EXP check out the video under Afficionado.
Since you need to play 3,000 matches of each game mode, this will come naturally. Check each individual game type medal for ways to idle boost. Check the video below for a more elaborate description on how to idle boost all game modes.
Same as "VETERAN" except you can play the matches yourself if you really want to win every one of them. You can also plug in a 2nd controller for the other team to even out the odds.
You can score headshots with most single-fire weapons. Easiest for me is to down someone, then fire 2 rounds in their head with the snub pistol. Other good weapons for this are the boltok pistol, the longshot or the torque bow. Video shows easy method with a 2nd controller. An elaborate explanation can be found here
) heavy weapon kills.
One-shot, Mulcher and Mortar counts as heavy weapons.
) explosive kills.
Grenades, Boomshot, Torque Bow and Digger counts as explosives.
You execute someone who is downed by pressing Y or X (meat shield) while standing next to them, chainsaw-kills and bayonet-charges also counts as executions and stack with kills for that weapon.
Skunk enemy team (25/100/500/2500
Win without letting the enemy team win a single round, cannot be won in 1 round matches. Recommend you to go for these while going for "Sovereign" and "Leader" medals or if you want them done as quick as possible, Warzone set to 2 rounds will be best. Must be done with bots set to "Fill" or in a match full of players. You won't get it every time but it will go up little by little.
) Untouchable ribbons.
You get the untouchable ribbon by finnishing a round of CTL as leader without letting the enemy capture you at all. There is a trick to make you leader every round, you need to have 2 controllers and a dummy profile. Make your dummy profile the main player by pressing start with the 2nd controller at the "PRESS START"-screen, this will make your dummy profile the main player and you the secondary player. Start a match of CTL with rounds to win at 1 and cap time at 10, the key here is to put both you and your dummy profile on the same team vs 5 bots. The first match you start will have the dummy as a leader but every match after that you will be the leader! Must be done with bots set to "Fill" or in a match full of players.
) enemy leaders.
Earned in CTL by grabbing the other teams leader for as long as it takes to win the round. Must be done with bots set to "Fill" or in a match full of players.
) assists in Versus multiplayer.
Damage an enemy and let a teammate get the kill. Will surely come by itself if you plan to play in real matches online, if not, wait till you knocked out all the kill medals, then play KOTH or CTL with insane bots, find a place with a good view of the map and just spot and spray with your lancer, letting the bots do the killing.
Press X while standing next to a downed teammate. These will most likely come while going for all the other medals, just revive whenver you have the chance. If you really want to knock these out fast, play CTL with a bot and a 2nd controller and turn friendly fire on. Keep hitting/shooting your leader till he goes down, then revive him, rinse and repeat.
) Buttoned Up ribbons.
You earn the Buttoned Up ribbon by spending the most time in cover in a match, using a meat shield will also count as cover. If you have a turbo controller you can get these while you let your game sit by putting something heavy on the a button. You'll get this medal every match this way. Must be done with bots set to "Fill" or in a match full of players.
) perfect active reloads.
Will most likely come naturally while going for kills, otherwise, the snub pistol is the fastest gun to reload, master it and spam reloads.
) Lancer kills.
Chainsaw kills counts as well.
) Hammerburst kills.
) Retro Lancer kills.
Retro charge kills counts as well.
) Gnasher Shotgun kills.
) Sawed-off Shotgun kills.
) pistol kills.
Snub, Gorgon and Boltok are the pistols. Try to pick up a meat shield so you can work on "CAPTOR" at the same time.