Impoppable tiles usually have bloon types and/or strategies that are very hard for players to counter with their current defenses. For example, if a player has recently started and can only hold back green bloons, a Ceramic tile will probably be labeled impoppable. An impoppable tile may be bumped down to a Very Hard tile when a player levels up. After a tile is rated as impoppable, its difficulty may be rated by the City Cash reward that the player would receive from it; the higher the reward, the harder the tile. For example, an impoppable ZOMG Tile near the center of the city might have a reward of File:City cash.png440 and send the first MOAB on round 13, but another ZOMG Tile on the edge of the boundaries may also be rated impoppable, but have a reward of File:City cash.png750, and se