The Act 2 World is lovingly referred to as the “upside down world” because it should be a completely opposite experience from the Act 1.
Where Act 1 explored all the things that were missing in the main character’s world, Act 2 explores all the ways the character’s world has exploded. Or, imploded.
If your world was quiet and sedate in Act 1, Act 2 is a wild rollercoaster ride.
If your world is Earth in Act 1, Act 2 is Pandora (think Avatar.)
If your world is a poverty-stricken district, Act 2 is the Capitol with its opulent wealth (think Hunger Games.)
Act 2 is where the MC can explore the theme, be someone different for a while, learn and grow.
Act 2 is where you deliver what you promised—a romance, an epic adventure, a mystery.