Rayman Fiesta Run

This achievement requires that you complete two El Stomacho stomach levels, where you are literally in El Stomacho's stomach. The first two you will encounter are Levels 26 and 27. This achievement is glitchy will not unlock until also completing the final two stomach levels, which are Levels 32 and 36. All of the completion achievements require ONLY that you complete the specified levels, which just requires reaching the end of the level without dying. This is quite easy on most levels, and even the ones where it can be a bit challenging, you can equip power-ups to make them easier. The most useful power-ups are the Hearts which allow to take a several hits before dying.

Level progression through the game is determined by how many unique Teensies that you freed. Teensies are "freed" by collecting a specific amount of Lums on a level and then reaching the end without dying. Each level has up to 4 Teensies that can be freed, with the last one requiring 81 Lums out of the 100 in the level to be gathered. Freed Teensies will contribute to the path that unlocks levels on the map. You can tell how many Teensies you have freed on any given level by the number of blue dots that fill a level's icon in the level-section map. For progression purposes, the Teensies must be unique (i.e. you cannot keep playing a level over and over to earn Teensies towards progression). A maximum of four per level will count towards progression.

With that said, as you play through the game from the beginning, you basically only need to get 3 or 4 Teensies freed on every regular level. Regular levels are the ones that have circular icons on the map. Once you complete a regular level with all 100 Lums collected, you will be awarded a crown and an "Invaded" version of the same level will unlock. These levels are basically the same, but are much more challenging due to many added obstacles and enemies. The invaded levels have a skull icon on the map and do not even need to be played as long as you focus on getting 3 or 4 of the Teensies from the regular levels as you progress.