One of the daunting problems in aquiring achivements for this game is that a lot of the achievements require multiple people to play. In order to get all of the achievements the minimum number of players needed is 10.

If you have ten coopertive friends, this shouldn't be a problem. However, if you're like me and can only get a maximum of four people in a room at once, there are some ways to get around the player requirements.

One option is to use multiple browsers, a cell phone and/or a tablet that can connect to the Internet, and controllers that can connect to the computer hosting the game. If there are friends assisting you, they can use their own devices, and you can reach any requisite number of players easily.

Another option, which may be easier to manage, is to use Multi-Account Containers[addons.mozilla.org] for the Firefox browser. Here, you can open a new 'container', which acts like a new browsing session, and log into a new account in each container.

For each achievement, I'll mark the minimum number of players needed to unlock it.

YDKJ 2015: Drain the Main Brain
Minimum Players Required: 1
All that needs to be done is to get all of the answers right in one episode. Here are the answers for the first episode:

1) Right (80%)
2) Right (the McConamiddle Ages)
3) Top (Ernie, Bert, The Count)
4) Bottom (Odette)
5) DisOrDat Round:
a. Left (Justin Bieber)
b. Right (Curious George)
c. Right (Curious George)
d. Left (Justin Bieber)
e. Right (Curious George)
f. Right (Curious George)
g. Left (Justin Bieber)
6) Right (Oddest)
7) Right (30 degrees Celsius)
8) Right (Albert Einstein)
9) Left (The Washington Malbecs)
10) Right (about 20 inches deep)
11) Jack Attack Round:
a. Gingerbread
b. Sticks
c. Rock
d. Adobe
e. Glass
f. Intestines
g. Cards

Once all of these have been answered correctly, the achievement is yours.

YDKJ 2015: Take It From Behind
Minimum Players Required: 2
This requires one player to score highly, and another player to beat their score during a Jack Attack.

Reference the guide for the "Drain the Main Brain" achievement above for the correct answers.

If you are having trouble getting this achievement, user 90 found this to work: "Turns out using the same names all the time doesn't work specifically for that achievement for some reason, so it only unlocked when i gave both players a completely new name each."

Please try this if the above method doesn't work.

Perform the following steps:
1) Answer question 1 wrong as Player 1. Do not let Player 2 answer.
2) Answer Question 2 and Question 3 as Player 2. Do not let Player 1 answer.
3) Either answer the questions correctly, or don't answer with either player for questions 4-10.
4) During Question 11, which is the Jack Attack, get all of the answers correct as Player 1, re-taking your lead.

After the end of the first round, this achievement should pop.

YDKJ 2015: Dat'll Do
Minimum Players Required: 1
If you are going for all of the achievements, this one will come with the "Drain the Main Brain" achievement, since this achievement must be completed in order to get the other achievement.

In order to earn this achievement, see the answers for Question 5 in the "Drain the Mad Brain" section above. Answer every question correctly.

YDKJ 2015: Winventory
Minimum Players Required: 1
There are 50 total episodes in You Don't Know Jack, and in each of them, there is a "Wrong Answer of the Game" based on the sponsor for that episode. Note that you will have to play until the very end of one episode to unlock a new episode. If you're not sure if you've selected the "Wrong Answer of the Game" before, if you have gotten the prize, a "present" icon will appear at the end of the episode's name, as well as the prize for the episode being displayed below the high score.

The "Wrong Answer of the Game" solutions are below:
1) Question 6: Left (Odder)
2) Question 4: Down (Lens Crafters)
3) Question 8: Right (Pop)
4) Question 3: Left (his big FEET)
5) Question 1: Top (the Greens)
6) Question 9: Right (Abbey Road)
7) Question 2: Left (a horde of zombies walking in circles)
8) Question 7: Left (What's Eating Gilbert Grape? (March 4, 1994))
9) Question 10: Down (She won't have another "time of the month.")
10) Question 6: Right (Brian)
11) Question 4: Down (The Wicker Man)
12) Question 6: Down (adding NEW SHADES to the hue of his wardrobe)
13) Question 2: Right (5000-****-****-0666)
14) Question 4: Up (a fuzzy octagon)
15) Question 7: Up (Don't Speak)
16) Question 1: Down (The Jolly Green Giant)
17) Question 6: Left (a POLKA DOT dinner jacket)
18) Question 7: Down (Mr. Burns)
19) Question 5: Down (Michelangelo's David)
20) Question 9: Right (mole sauce)
21) Question 3: Left (Pinocchio)
22) Question 1: Left (the March Hare)
23) Question 9: Up (The Backyardigans)
24) Question 5: Right (Planet Hollywood's)
25) Question 7: Up ("Giant Monster Rodent Infestation" coverage)
26) Question 7: Right (dropping the kids off at the POOL)
27) Question 2: Left (yes's and no's)
28) Question 9: Left ("Head cheese is the cheesiest!")
29) Question 1: Left (Dwayne Johnson)
30) Question 6: Left (Brady BUNCH)
31) Question 7: Down (a Peeps polar bear)
32) Question 6: Down (Atlas Shrugged)
33) Question 3: Down ("I showed an old lady my FOIL...")
34) Question 3: Right (Mafia)
35) Question 3: Left (Pirate's Booty)
36) Question 8: Left (chicken fingers)
37) Question 2: Down (craps)
38) Question 6: Down (the Chicago BULLS)
39) Question 10: Right (a SWISS CHEESE Sarah Michelle Gellar)
40) Question 6: Up (Abraham Lincoln's ear)
41) Question 4: Left (cardboard pope hats)
42) Question 1: Down (52-card pick-up)
43) Question 2: Right (Beaker)
44) Question 5: Down (SWF seeking JFN)
45) Question 1: Left (Contact)
46) Question 8: Up (Ciao Ciao)
47) Question 7: Up ("No matter what you do, don't let any BOXERS in.")
48) Question 2: Down (Bruce Wayne)
49) Question 6: Left (in the seat NEXT TO me)
50) Question 7: Up (lots of extra closet space)

Politician
Minimum Players Required: 3
This requires all players to pick your lie.

Enter a wrong answer as Player 1, and have Player 2 and Player 3 pick the answer that you wrote. This will unlock the achievement.

Truth Fairies
Minimum Players Required: 2
This requires all of the players to find the truth on a question.

If the correct answer is known, make sure all players choose that answer. If not, it can be easy to have all players enter an obviously wrong answer (such as "abc"), and pick the obviously correct answer from the lot.

Copycatfishers
Minimum Players Required: 2
This requires two players to enter the same thing as another player. Ensure that two players, either a friend or another instance of your account, input the same response. When this is done, the achievement will pop.

Don't Know What To Believe Anymore
Minimum Players Required: 2
When entering an answer, input the correct answer for that question. This can be done by looking up the answer, or by knowing past answers from previous games. Once the game says that the player input the correct answer and must input something else, this achievement will be earned.

Goodfinger
Minimum Players Required: 3
Someone must create a drawing that everyone else guesses the prompt to correctly. Once everyone has done this, the achievement will pop up.

Show Me the Monet
Minimum Players Required: 3
This requires a player to win by over 3,000 points. Have Player 1 answer all drawings correctly, and have Player 2 and Player 3 answer all questions incorrectly.

S​c​h​m​u​c​k of the Draw
Minimum Players Required: 3
For this achievement, everyone has to pick the incorrect prompt of one player, i.e. Player 1 should enter an incorrect answer, and Player 2 and Player 3 need to select the incorrect answer that Player 1 entered.

"Art" Connoisseur
Minimum Players Required: 3
This requires the player to select the correct answer on every drawing prompt. Remember the drawing prompt, or write the prompt as the picture, and then pick the correct prompt for the entire game.

Squish, Nothing But Wet
Minimum Players Required: 1
The player must get one round completely correct during a full three-round game. The player can look up the answer, or the player can take an educated guess. It's about a 50/50 chance after all, isn't it?

Blufforgy
Minimum Players Required: 10
Have 10 separate players join the game. Once the correct number of players is on the register, this achievement will be unlocked.

Tri-Swatter
Minimum Players Required: 1
Simply play the game and win it to unlock this achievement.

"What's My Name?" ft. Bugs
Minimum Players Required: 1
This requires a player to enter one of seven special names as their player name. Enter one of the following seven names as your player name to get this achievement: Barb, Chester, Gus, Lars, Skippy, Sparkles, Twitch.

Word Herd
Minimum Player Number: 8
Get eight players to register to the game. Once eight players are registered, the achievement will pop up.

Group Hug
Minimum Player Number: 2
Have two players, Player 1 and Player 2. Have Player 1 enter a word, and have Player 2 say that they like it. Afterwards, have Player 2 enter a word, and have Player 1 say that they like it. Go back and forth like this until the game is finished.

Spud Stud
Minimum Player Number: 2
Create two players. Have Player 2 accept all of Player 1's words, and have Player 1 reject all of Player 2's words. Do this for all three rounds to unlock this achievement.

Golden Nugget
Minimum Player Number: 2
Have Player 1 type the word "nugget" without quotation marks. Have Player 2 accept the word. This achievement will then be unlocked.

Version 1.4
--Fixed question 28's number for "Wrong Answer of the Game" courtesy of Ashthulhu.--

Version 1.3
--Fixed a missing question & typo for the You Don't Know Jack achievement with thanks to sh_rryy. Fixed the first step to getting the Take It From Behind achievement with thanks to Amoyensis.--

Version 1.2
--Added unlock details to Taking It From Behind. Thanks again, 90!--

Version 1.1
--Changed required number of players for Tri-Swatter from 2 to 1. Thanks, 90!--

Version 1.0
--Created guide--

Please let me know if anything needs to be clarified, if you have any questions, if you have something to add, or if there are any errors.