I think most of the enemies in Super Mario Bros. are trying to teach you a lesson. Goombas are the basic enemies, Koopa Troopas teach you that you can throw enemies, Spinies show you that you can't jump on all enimies, Piranha Plants show you that enemies can come out of pipes, and buzzy beetles show you that you can't throw fireballs at all enemies. The only 3 I'd say that can't be applied to a lesson are Hammer Bros., Lakitus, and Bowser (If you want to count him). They're just too complex.