Captain Britain’s token is unlocked after completing his mission, ‘Trouble Brewing’, on the steps of the Lincoln Memorial in Washington D.C. for 250,000 studs.
Union Jack’s token is located on a roof in a locked box in the S.H.I.E.L.D. Base. You need to use Black Widow’s stealth ability to activate four switches on the ledges on the side of the building to open the box. Collect the token and purchase it for 75,000 studs.
Spitfire’s token is located in a blue container on a roof next to a building surrounded by eight switches in the Novi Grid Town Square in the Sokovia Hub. Use Quicksilver to jump on a Speed Boost Pad and run around the building activating all eight switches, which opens the box. Collect the token and purchase it for 30,000 studs.
Agent Carter is automatically unlocked after completing the level ‘Anger Management’ in Story Mode.
Mandarin (Trevor Slattery) is unlocked after completing his mission, ‘Pandering to Mandarin’, on the beach (near the blue platform) of the Malibu Hub for 3,000 studs.
After you’ve unlocked and purchased all five characters, hold
to bring up the character grid (if you can’t do this yet, visit a blue or red platform). Then select one character to spawn. Repeat this process four more times for the remaining characters. Once you select the fifth character, the achievement will unlock.