Level 21 is the eleventh level in Amber Alley and the ninth Firefly level in Diamond Digger Saga. To pass this level, you must wake up 1 firefly and reach 2,500 points in 10 moves.
There's very few moves, although you don't need many to pass the level.
You have rockets - it's most likely that the one at top right corner won't be usable, and also it's very likely that the one at the top left corner will be. Use the one that you can match. Afterwards, focus on destroying the required ground blocks, so that you can bring the flow of water to the firefly, your target.
The 1-star target score used to be 4,000, leaving a possibility of failing the level with not enough score, although it is uncommon.