Sooner or later, platformers designers will introduce some collectible Coins/tings/star bits into their game.

Their role of increasing our score move or less belongs to the past how, but a game that has no collectibles feels a bit odd. I know because I just played "Gris" which has none, and having sequences where you slide down and jump at will but have no incentive to do so because there is no "coin" to find was unusual. In fact, it made the game feel -artistic- instead of playful. Collectibles may play roles other than making the experience more fun, though.  They can guide the player, if you  make sure that you never put some in places that cannot be reached.  That's quite an obvious one. They can invite the player to try something  more difficult than they' d normally do, and they can let the player know whether they have already visited some locations.  The question Neutronized raised is whether we should allow the game to feature some collectibles that are  impossible to skip. I see a few occasion where this Could occur, like having a long line of them on a platform and no way to stand between them, "or having them drawing a wall". If you end up designing something like that, I invite you to think  again: what does these extra collectible bring to your player" You removed them the freedom of  whether they pick something or not. It's like forcing a kid to eat some chocolate whether the...