LEGO Marvel Super Heroes

The real question this achievement is asking: Where are the stud multiplier Deadpool bricks?

x2: Unlocked at the start. Costs 1,000,000 studs. Should be the first thing you buy in the game.
x4: Found in the Daily Bugle, which is unlocked with 10 gold bricks and is a bugle icon on the map. Use a telekinetic to rearrange the trophies in the room. If you're doing this as soon as you can, you can buy Mandarin before Jean Grey is available. Costs 2,000,000 studs.
x6: Found in Feeling Fisky, which is unlocked with 50 gold bricks and is a staff with a diamond icon on the map. Use a telekinetic and a heat beam character (Iron Man Mark 42, Human Torch) in the back right corner of the map. Costs 3,000,000 studs.
x8: Found in Reptilian Ruckus, which is unlocked with 125 gold bricks and is a lizard icon on the map. Use a lightning character (Thor, Storm) to charge up the electric switch on the lower level, then use Magneto to open the cage containing the brick. Costs 4,000,000 studs.
x10: Found in House Party Protocol, which is unlocked by beating the story and found at the top of Stark Tower. You'll need a telekinetic like Jean Grey; break open the pinata in the back between the DJ booth and the dance floor. Costs 5,000,000 studs.
Collect Ghost Studs (Optional): Found in A Shock Withdrawal, which needs a puzzle solved by a smart character to unlock. Use a heat beam character to blow up the money next to the bank truck. Costs 100,000 studs.

Since you'll be getting them in free mode, once you get the bricks and optionally Stan Lee in Peril, you can save and quit and it'll count. To actually unlock the extras, you need to go back to the Helicarrier, enter via elevator, take the back left room like you're going to the character creator, but take the first right in the hallway to go to Deadpool's room. The interaction point with the TV lets you buy extras.

Now, if you're doing this late in the game and you have 125 gold bricks, this will come with normal play. Just turn on all the multipliers and do what you want.

However, the earliest you can get this done is without the x8 multiplier, and the rest can be done by 50 gold bricks. With the rest, that gives you a x480 multiplier. You'll also need Collect Ghost Studs and a large muscle character like The Hulk or Abomination. Travel to one end of the map, then open your map and set a destination for the other side of town. Sometimes, the guide won't show up if you start in the city and plan to run into the X-Men school, so choose a closer location until the guide appears. Then use your muscle character to just run in a straight line collecting all the ghost studs. All together, each stud is worth 480,000; each run from one end of town to the other netted upwards of 100,000,000 studs.

If you're looking to actually complete whatever gold brick or character token you ran to, don't use The Hulk or Venom. Holding lets you change characters, but with them, they simply transform. You'll have to use your second character or find a vehicle spawn point to switch. Alternatively, use a different muscle character like Abomination or Colossus. (Alternately, you could hold during the transformation to bring up character select, but I found using someone else preferable. Thanks for the reminder, Ryno L!)

If you haven't done it already, use the time to bodycheck and destroy cars along the way. You don't even have to attack, just running into the car will destroy it in no time.

It might be worth noting that your stud counter has to read 1 billion for this achievement to pop. If you earn 500 million and spend them, then earn another 500 million, this will not count.
I thought it meant, through the lifetime of play, you have to collect 1 billion, and so was confused when I hadn't got it.