As I was enjoying my free week of Super Mario on Switch, I found it interesting to compare how we are introduced to Koopa Troopa mechanics in Super Mario episodes. Because, yeah, I'm fond of Koopas mechanics. 
Koopas are dangerous, but you can turn them back at their allies (same for dumbladors, you'd say). And you can dispatch many of them at once that way (unlike dumbladors) if you follow it closely enough. But then it can trick you if it bounces on a wall.In SMB1, you're welcome to kick in and dispatch 2 goombas, then another 4 if you're running after the shell, but then it will bounce back at you. To some extent, your first experience with Koopa Troopa is the full experience. Dangerous/helpful/treacherous. You're warned: this is what the game has for you. You'll have to clear about one half of that level before you can see your first koopa, though. And you can easily miss the only one of the level if you take the secret pipe.
SMB3 comes with something new for you. Koopas shells can now be used to unlock contents of question blocks that lay on the ground. This can be discovered from the very second screen of the first level!
 Note how you can decide not to face it by sneaking under the green block or escalading the pink and white blocks to easily jump past it. Note, too, how the shell bounce on the question block may be harmless as it will be cleared out through that 'under green block' route, optionally dispatching a goomba. (That might possibly be a bit too m...