During one development, we focused on hardcore strategy, but 90% of new players left within 3 days. Later, we added "light mode" and "newbie map", and the retention rate increased significantly.

The solution is different in each game, but here’s a couple of my thoughts:

• Have multiple solutions for each problem. Is there a giant ogre guarding the entrance? Maybe there’s also a hidden entrance. This way newbie players can still progress in the game, but more hardcore players might decide to take on the extra challenge of the ogre instead.
• Make harder challenges optional, but with rewards, so players will be more likely to at least give them a chance.

My suggestion is to make levels whose difficulty starting from beginner to hard then allow players to choose which level to play. This way newbies could start by playing easy levels while hardcore players could jump straight to hard levels.

Good ideas all around! I would suggest allowing hardcore players to "flex" a bit, either through an achievement system or a handicap setting. A casual player can play the game just fine from start to finish without having to select "easy mode" and feel like a noob, but a hardcore player can 100% or speedrun if they so choose. Beat the next level without jumping, or only using one kind of attack, or in "melee only mode". Agreeing with Afloof.dev, optional challenges that make hardcore players feel like they accomplished something, without alienating new players or making them feel like noobs.

Thanks for the great ideas. I struggle a lot on setting the difficulty in my games; especially action ones. Testing our game many times makes us, game devs, very proficient at playing it.

If a game has high scores, you can raise the difficulty based on the current player achievement thus creating a dynamic difficulty curve.