Complex sentence: Prior to starting full development, the developers designed a playable 2D prototype similar to the original "Zelda" to experiment with physics-based puzzles; the game uses a modified version of the Havok physics engine.
Split into simpler sentences: Prior to starting full development, the developers designed a playable 2D prototype similar to the original "Zelda" to experiment with physics-based puzzles. The final game uses a modified version of the Havok physics engine.