You'll unlock everyone naturally, stay safe, and keep your account.

: The pact holds forever; every new Legend added in the years to come is automatically delivered to the player's account. Legitimate Rewards Every FREE Item & Code In Brawlhalla (2024)

If you just want to play a character to see if you like them, you don't need to unlock them at all.

Check your mission log regularly. Missions reward you with Gold for completing specific tasks (e.g., "Knock out 3 opponents with Side-Sig").