There are 16 levels in Tiny Knight, some of which are boss levels. In regular levels you need to find all the crystals for Gold completion. This guide shows where those are. In the boss levels it's enough to beat the bad guy. There are videos and tips for that below as well.

A few general tips:

• Jumping on top of enemies is often just as effective as hitting them. Except if they are warriors and have a helmet, then the helmet hurts once.
  
• Let the enemies hit each other. It's often more effective than hitting them yourself.
  
• Shooting enemies cannot shoot lead, so stay on the move and they'll miss constantly (and hopefully hit each other instead).
  
• Crystals are often hidden at the corners or behind them so check every nook and cranny! Or check the videos below instead.
  
• Almost all enemies drop crystals, so don't forget to grab them! Only mushrooms and golems don't drop crystals.
  
• That said, don't let the crystals of the enemies fall below edges into the (occasionally fiery) abyss, or you'll have to rewind/restart the level.

Good luck and happy knighting!

You probably won't have any problems with this level but here's a video anyway for completeness.

Apart from a couple of puzzles, you should still be fine. You may ignore the running mushrooms, and close in on the archers and spitting plants indirectly so they'll miss you.

A video for completeness.

The Cavern level has even a couple of secrets, though they are easy to notice.

The video shows everything. I messed up once, sorry for that, but it goes to show that the wizards shoot straight at you so beware of them, especially that one.

As of Jan 10, there's a glitch that sometimes makes some of the crystals to disappear if you skip the cutscene, so you probably should just watch it anyway.

There's another simple puzzle in this level. Otherwise, this is a straightforward level. Don't miss any of those crystals in the arena fights!

Let him try to hit you, dodge, and he'll call his mushrooms. Use them to jump on his head. Repeat until he's down.

While you get crystals from killing the spitting plants, you don't need to kill them and collect them, though it makes it easier to fight the main monstrosity.

Very straightforward level crystalwise, but beware of the jumps over the chasms (as I conveniently oops demonstrate here).

Because of the many passages and the crystals camouflaging in the snow, be keen in this level. Once again I humbly show that it's not to be ashamed to die once or twice in the spinning traps.

Note especially the secret area at the end of the level, right next to the goal.

When he charges you, go towards a blinking wall. Let him hit one of those and he gets a rock to the head. Rinse and repeat, but don't let his ice strikes, thrown rocks and the global colding hit you. You may avoid the global colding by climbing on one of the larger rocks.

Pretty straightforward level. Always go towards the crystals. The couple of 3D platforming parts may prove frustrating, or not if you play better than me.

Puzzleish level, you have to turn on all the crystals. You may ignore the golem thingies if you'd like.

By the way, don't let the big fella at 1:10 part of the video fall down or you miss out on his crystals. Go towards the wall so when he charges, he'll hit that instead.

Dragon's Lair, or Dragons Lair as it's written in the game, contains this cute little dragon chicken. When he lands, go and hit her. Just don't let her or her spawn burn you. You should probably kill all the spawns when they appear, so they won't bother you too much.

Sorry for the video quality in this one. For some reason there was a constant loading sign in the foreground that was extremely annoying and results in a blinking video.

I consider this one of the more difficult levels. There's 3D platforming on rising and lowering platforms and even a mini boss.

For the mini boss, you should stay on the move and if possible, keep watching the thing so you can better avoid its spit. It dies when all four ballistas have shot it. Don't let any of the crystals from the enemies fall into the lava though.

The longest and glitchiest level in the game. Avoid the stairs and side routes because they often contain glitches that require you to restart the level.

The first island (when you land) contains 37 crystals, the rest of them up until 121 are on the second island.

Don't forget to pick the one in the tower, it's quite well hidden since the camera just barely sees it (at around 5:18 in the video, top-right).

There are 11 crystals in the sewer. Finally, you should head to the last island when you have 161 crystals, the rest of them are there.

Make sure that none of the enemies or their crystals fall into the water or you'll have to rewind/restart the level.

Straightforward level with some spinning traps. Tread carefully and you'll be alright. No crystals are well-hidden.

The arena level basically. You'll have to beat a whole lot of skeletons here. Make sure you don't miss out on any of the crystals they drop.

The cannon cutscene is glitched, so if you skip it, the level might become unbeatable and you'll have to restart, so just let it run its course. At least there's a cartoon explosion to enjoy.

Here's the main boss, the Skeleton King! He's the most difficult boss in the game. Not too difficult but his attack patterns change a lot so you might be surprised and die a few times before beating him.

He's invulnerable until four of his henchmen die, so kill those and then go poke him with your sword.

In the first phase (i.e. before being hit at all), he just waltzes at you and lunges with his sword. Let him take a swing but dodge it, so enemies spawn and kill those.

In the second phase he charges. Dodge and let him swing at you again to get mobs to spawn and kill.

In the third phase he charges and does ground smashes. Keep a look on those smashes and jump when he does one to avoid damage. It can be handy in killing mobs though.

In the fourth phase there will be some undead tentacles in the edges of the arena. Avoid those areas. If there's a shooter there, shoot them with your fire sword. The king also does his ground smash twice in a row in this phase.

Fifth phase is similar but he does ground smash only once.

In the sixth phase (and last) phase four skeleton mages appear. Avoid damage and kill them and you may give the final strike and beat the game.

Hopefully you found at least parts of this guide useful. And if you did all of it, gratz on beating the game!