The Neo Geo Pocket was one of the many short-lived handhelds that fell to Nintendo's domination of the handheld market and there was a Sonic game for it. Sonic the Hedgehog Pocket Adventure is almost like a remake of Sonic the Hedgehog 2 using Sonic 3 music. It is also the first Sonic game made by Dimps, who would go on to make almost every other portable Sonic game.
The levels all correspond to Sonic 2 levels, but shuffled up a bit. The level design is even much the same in some stages. Here is the level map of Pocket Adventure's Aquatic Reflex Zone and here is a level map of Sonic 2's Aquatic Ruin for comparison. While they are not exactly the same, they are very similar.