Second Dimension (known in the game's code as Hard) is a medium-difficulty Level in Open Hexagon. It can be thought of as Open Hexagon's equivalent of Hyper Hexagoner, though it is slower than the latter, and pulses less.
Second Dimension's officially given difficulty is Hard. It can be thought of as being medium difficulty, however. It may seem daunting at first, but it is easy to get used to. However, the relatively high speed still allows for little to no lag (which can cause many players to become unable to survive long on this level without a decent frame rate) as well as very few mistakes.