I'm playing Diversion for android and have compiled a full list of the double-gem character that works for each level. The way they work is simple: you just choose the indicated character before playing the associated level and you'll earn double the gems at the end.

In the early days we had to keep an eye out for a blue "character" disc floating somewhere down-low in the level (very often right before the end) and figure out how to get your character to fall into it. Beginning with version 1.41, the double-gem character is always just revealed on the level's end screen, so there is no more blue disc to fall into. The game even helpfully defaults the character list to that character when you click on the character-changing icon, making it easy to choose and/or buy.

If you're just starting out, I'd recommend that you just enjoy the game for a while without obsessing over double gems, or even being overly hung up on getting all 3 stars. Once you've gotten the hang of things, its nice to come back later (which you have more characters) and do the levels again with an eye to maxing out the gems.

You may also be interested in some ezonecom walkthrough videos, some walkthrough videos by Michael Rigoni, and a text walkthrough for the various levels.

If you have corrections/additions/etc., feel free to .

A huge "Thank you!" goes out to Catherine Poole, who has been immeasurably helpful in updating this list as it has grown over time.

Each of the Endless Bonus levels (above) are unlocked when you get a certain character:

The following codes can be typed on the reedem page for fun and profit (though it has been reported that Diversion for Apple's iOS devices have stopped accepting cheat codes, so these may be Android only these days):

Here are all the characters that I know about: