After defeating the Hand of the King, you unlock Boss Stem Cells (BCs), increasing the game's difficulty. Each BC adds new enemy types, modifies existing ones, and introduces new mechanics like malaise. Higher BCs also unlock new biomes and blueprints. The game truly opens up at 1BC and beyond. Don't rush; take your time to master each difficulty level before moving on. The jump from 4BC to 5BC is particularly significant.
