Regular enemies are common opponents in the Kirby series. They can usually be easily defeated in one or two hits. Starting from Kirby's Adventure, certain ones give Kirby a Copy Ability when Inhaled, while others do not (these enemies are referred to as ability-neutral enemies). Most of them come back even if they are just defeated a short while ago should the screen scroll back to where they are; almost all of them reappear if the room was exited and re-entered through a Door. Only special ones like UFOs or Crets do not reappear until the whole level is restarted, and certain ones are immune to every form of attack, so avoidance is often the best way to proceed.
It is never revealed why so many of Dream Land's inhabitants would want to impede Kirby's progress, as Kirby always ends up helping them in the end. It can be assumed that they are inherently evil or have loyalties to Kirby's opponents, such as Waddle Dees to King Dedede. In most other cases where enemies are not native to Dream Land, the motivation -- such as loyalty to or influence by Dark Matter -- is much more obvious.