How about some sort of puzzle locks to enter big boss layers.

Idea:

Find clues in the maze to figure out how to solve the combination.

Puzzle locks and traps on high level chest that contain artifacts.

Idea:

Some sort of lock picking game where if you, screw up and get a big breath of blue poisonous cloudy mist.

Well, a lot depends on how mean (?) you want to be with the puzzles.  Here are a few questions I would pose for the community to ponder:

1. Will the requirement to get to the treasure be solving a puzzle or else the killing of one or more creatures?
2. Do you envision unlocking the treasure puzzle in order to help us defeat the boss of that level, or
3. Do you perceive that the treasure will be a reward for defeating the boss (awarded after killing him).
4. Or, do you perhaps see the treasure for a boss to be found on the boss's level or else on the next (tougher) level?
5. Does each level require one of these puzzles or maybe just on a few select ones, such as level 5, level 10, level 14, etc.

In my opinion, I am in favor of the following: 1) puzzles and kills, 2-3) get treasure after boss is killed, not to help defeat the boss, 4) Reward found on next (tougher) level, 5) Only on select levels, not on all.

FDWojo (I don't know why the numbered lines are a lighter gray than the rest of the text. I can't fix it. There's no place to select text color. Ideas?)