The Bear is a special kind of Item that appears in Triple Town.  It moves one space every time you place an Item, blocking you from placing an another Item where it is.  A Bear turns into a Tombstone when it is trapped (when it has no more spaces it can move to), or when an Imperial Bot is used on it.  When there are three Tombstones adjacent to each other, they form a Church.

Therefore, while Bears can be quite frustrating, there are many uses for them.  In the town, "Dangerous Forest", there are 50% more Bears.  In "Peaceful Valley", there are no Bears.  It's common for a player to have many Bears at once, thus making the game more challenging.