Marvel Super Hero Squad: The Infinity Gauntlet

This is definitely the most painful of all the achievements to pick up in this game, if purely for a handful of challenges. If you've got a friend you can play through most of these challenges with it'll make life a helluva lot easier, but it is definitely possible to pull off solo as I just finished it off by myself just now. All the notes I'm adding below are under the assumption you're flying solo.

Some of the challenges are unlocked by completing various characters Heroic Feats, so you will need to complete a number of Heroic Feats before you get this achievement.

Survival
I used Thor for all of them, throwing his hammer and just using his Heroic Attack when things get way too hectic, as they will towards the end of the time limit.

Soar-N-Score!
Asteroid Field and Base Jump: These both play out just like their respective segments in Episodes 1 and 7. Just collect some gems as you fly through the stages and survive to the end of the level.

Galactus: Now this is made a lot harder than when you battle him in episode 8 because of the fact that you don't have an ally, and the fact that it only takes two hits to be KOed, and thus fail the challenge. The best way to handle Galactus is to stay in the centre of the screen for as long as possible as that gives you the best position to dodge both his swats (left and right) and his eye lasers (top and bottom). He will sometimes give you a vocal prompt on what he's about to do, so pay careful attention to that, but in the end you'll be able to visually see what he's about to do next. Just feed him until he's full and victory is once again yours.

Blast-A-Thon!
Whack An Imp: I can tell you that this was by far the most frustrating of the challenges for me, if mainly because I used Thor for it. Thor seemingly doesn't have the ability to destroy incoming bombs or rocks being thrown at you, but Iron Man definitely does, so I would suggest using him for minimal frustration.

The best idea to get through this is to start in the centre of the screen, fly straight to the imp, fire, and move immediately back to the centre. That will give you more than enough time to line up the next imp before it fires for at least for the first minute. After a while you won't really have time to return to the centre as you'll just be constantly moving from imp to imp, but do continue to try to get back to the centre if you don't see the next imp. There are a couple occasions where you will get a mini break, which of course you can use to get back to centre.

Edit - JCKellner has passed on this even simpler solution to beating Whack An Imp. Thanks JCKellner.

"Blast-A-Thon Whack An Imp - another site suggested using Nova once the first Imp shows up, don't shoot it, but, shoot the things it throws out of the sky and once the clock is close to zero then kill the Imp. This lets you finish this challenge with only killing 1 Imp. Found this on xbox360achievements.org in their guide."

Radar Riot and Earth's Orbit: These both play out just like their respective sections in episodes 4 and 9. Just head straight for every bug/missile as you see them and blast away until the time expires.

Defender
The tactics I used here were similar to what I used with Survival Mode but there are a couple specific tidbits to each as the idea of Defender is not only to survive the time limit, but to allow whatever you're defending to survive as well. In each case, I again used Thor.

S.H.I.E.L.D. Building Rooftop: Stand in the centre and just throw Thor's hammer at every doombot as they come, using his Heroic Attack when things get hectic. You do not need all 3 vents to remain intact, just as long as one is still intact at the end of the time limit.

Lost In The Negative Zone: Just stay next to the little robot and fire Thor's hammer at all the bugs that come your way. If they start to get too close to it, use your Heroic Attack. The robot has 4 units to repair so you will have to move with the robot 3 times throughout the challenge. If you somehow still have time remaining when the robot has completed repairs on the 4th unit, it will run away and it will basically turn into a survival mode stage from that point.

Battle Floats: Again, throwing hammers and Heroic Attacks is the ideal way to deal with this. You'll be defending 5 statues here. As the stage progresses, you will get prompts in the bottom right hand corner of the screen telling you whether the attacks will be concentrated on the left or right hand side. Follow said prompts when they pop up. Again, as per the S.H.I.E.L.D. Building Rooftop stage, only one statue needs to remain standing to complete this challenge.

Super Smash
All you need to do in each of these is just to destroy an object, and let the time limit run out.

Iron Man Robo Racing
Here you are required to beat the top score on every race. Only Track Mark I is unlocked to begin with, but as you beat each of the times, you'll progressively unlock Marks II through VI. Completing Track Mark VI with a faster time will also unlock the Robo Racer Achievement.

Hack Attack
Like Iron Man Robo Racing, you are required to beat the top score on each of the Circuits. Again, only Circuit I will be unlocked to begin with, but as you beat each of the times, you'll progressively unlock Circuits II through VI. Completing Circuit VI with a faster time will also unlock the Elite Hack Master Achievement.

Once they've all been completed, you should have Challenge Master :)

Guide courtesy of http://www.xbox360achievements.org/game/marvel-super-hero-sq...

As you play through story mode and complete various feats you will unlock mini-games for play in the “Challenge” section of the main menu. You need to complete them all for this to unlock. They are considered “complete” when you have the top score. Here is a list:

Survival

Skrull Ship Aft – Kill the first guy and then run to a corner and block until the timer runs out.
The Colosseum - I used Thor and just kept throwing my hammer along with a heroic attack when needed. I was able to use a green gem on Hercules to take him out in 1 hit.
Bug Rush - I used Thor and just kept throwing my hammer along with a heroic attack when needed. I was able to use a green gem on Annihilus to take him out in 1 hit.
Asteroid M Elevator - I used Thor and just kept throwing my hammer along with a heroic attack when needed.
Construction Site – Kill the first guy and then run to a corner and block until the timer runs out.
New Zenn La - I used Wolverine and played as cautiously as I could. Using blocks and then counter attacks to fill my heroic meter. I got some major help by getting 2 back to back SHS badges and a lot of time stones. Of course these drops are random.

Soar-N-Score

Asteroid Field – Fly through the course and make it to the end without dying.
Base Jump – Fly through the course and make it to the end without dying.
Galactus - This is a repeat of the boss fight. The same tactics apply so check "The Large One" for help if needed.

Blast-A-Thon

Whack an Imp - Choose Nova as your character and when the first Imp pops up, DO NOT shoot him. Instead, move your cursor away from him and shoot whatever he throws at you. Now just hold down X at that exact spot and he will keep tossing items at you while you keep shooting them out of the sky. Just sit there and wait until the countdown reaches zero and no other Imps will even spawn. Thanks to weffalump for this great tip!
Radar Riot – Live through the entire fight by shooting things out of the sky until time runs out.
Earth’s Orbit – Live through the entire fight by shooting things out of the sky until time runs out.

Defender

S.H.I.E.L.D. Building Rooftop - I used Thor and just kept throwing my hammer with Y. Use your heroic attack in a pinch.
Lost in the Negative Zone - I used Iron Man. You need to protect Herbie while he repairs things. I just stayed beside him and kept blasting with my repulsers and I would use a heroic attack when things got hectic or on the large bugs.
Battle Floats - I used Thor and just kept throwing my hammer with Y. Use your heroic attack in a pinch.

Super Smash

Skrull Shenanigans – Destroy an object and then just stand there until time runs out.
Sparring Pit - Destroy an object and then just stand there until time runs out.
The Cake Nightmare – Destroy an object and then just stand there until time runs out.
Grandmaster’s Stage - Destroy an object and then just stand there until time runs out.
Magneto's Observatory - Destroy an object and then just stand there until time runs out.
Spire Pinnacle - Destroy an object and then just stand there until time runs out.

Iron Man Robo Racing

Track Mark 1 – race around the track 5 laps with a time better than 1:20
Track Mark 2 - race around the track 5 laps with a time better than 1:30
Track Mark 3 - race around the track 5 laps with a time better than 1:40
Track Mark 4 - race around the track 5 laps with a time better than 1:10
Track Mark 5 - race around the track 5 laps with a time better than 1:20
Track Mark 6 - race around the track 5 laps with a time better than 1:10

Hack Attack

Circuit 1 – align the shapes to connect a green line. You need to beat 0:14 for this one.
Circuit 2 – align the shapes to connect a green line. You need to beat 0:18 for this one.
Circuit 3 – align the shapes to connect a green line. You need to beat 0:20 for this one.
Circuit 4 – align the shapes to connect a green line. You need to beat 0:38 for this one.
Circuit 5 – align the shapes to connect a green line. You need to beat 0:40 for this one.
Circuit 6 - align the shapes to connect a green line. You need to beat 0:50 for this one.

I just want to add one piece of advice for the "Survival" mode challenges. For all of them except "New Zenn La" I just plugged in three controllers and had Thor as my primary character and Scarlet Witch as my two controllers who just blocked all the time. With a little luck this strategy worked fine (success in five attempts or less),

"New Zenn La" was a different story because Dark Surfer goes through shields, so how I eventually did it was go through as Thor (with no blockers). The strategy was just to make sure that I didn't get sucked into the green holes (which creates a tough clone of you). With no clones, the average monster is a one or two hit kill and Dark Surfer can be beaten with some patience. Even with this strategy, it was still not a walk in the park. As well save your Heroic attacks when you are getting surrounded.

Tip when doing the Survival challenges, you can use (2) controllers and just hold down block the entire time frame. I did it with Scarlett Witch and used her bubble shield, but make sure in the last few seconds to at least attack an enemy to get a score.
This method DOES NOT work on the last survival challenge against Silver Surfer. I used Thor, it's honestly the luck of the draw of which infinity stones pop-up, but if you can get the purple, green, orange stone then you are golden. If you face an enemy with the green stone, I would just quit out and retry, green means instant death on hit. Takes a few play throughs until you get the right stones to give you the advantage.

Also try to stay away from the green portal from making copies of you. Try to stay opposite of the map to avoid being pulled in.