Diamond Digger Tips #1: Eyes on the prize
The goal of Diamond Digger is to get any diamonds to the bottom of the screen. You can only claim victory when all of the diamonds reach the bottom. However, during testing, I've seen a few people seem to forget this goal.
Take this puzzle for example:
(Larger numbers crush smaller numbers)
There are a lot of blocks and a lot of possible things to crush, but the only things you really need to pay attention to are the diamonds in the middle. Your focus should be making moves which either bring them down the screen or line things up in order to bring them down the screen on a later move. Other things crushing each other is irrelevant.
Diamond Digger Tips #2: Method to Madness
On the vast majority of Diamond Digger puzzles, what looks like a vast clump of blocks holds a very simple solution. At the very least, there's one thing that's you're trying to do that goes beyond getting the diamonds to the bottom of the screen (but ultimately results in that).
For example:
This is rather a simple one and the solution is fairly obvious, but the principle is applicable to a lot of other puzzles. Your aim here is to get the metal block to crush a stone block, only then can you slot the diamonds through the bottom row. A fair few puzzles have a similar idea, where, although it might not be getting a piece of metal to the bottom of the screen to feed the diamonds through, there is one block that you need to get to a certain position to proceed with the level.
Diamond Digger Tips #3: Don't kill it until it's over
While watching people test diamond digger, one of the most cringeworthy things I see is people resetting puzzles from states which are still solvable, in a couple of cases only two or three moves away. Up to a point, it's a lot more efficient to be resilient with the puzzles.
For example:
(I'd flipped the numbers when taking this picture, so in this one lower numbers crush higher numbers
This is a half finished puzzle and a position in which a lot of people I've seen testing would give up on. Moving the second row from the bottom to the left or moving the bottom row to the right wouldn't cause a drop and the row would bounce back. At this point, realising that the diamond is too far away from the metal, some people would give up. However, by manipulating the above rows, you can still solve it from here, you just need to shift the rest of the blocks into a position which would cause a drop to occur when you move the second row to the right.
Diamond Digger Tips #4: ...but know when it's over
Flying in the face of yesterday's tip, it's also worth being actively aware of when a puzzle has become completely unsolvable.
There's actually quite a simple way to work a lot of cases out. If there is are blocks all the way along the bottom row (no gaps), there are no blocks of metal (diamonds crush metal) left on the board and there are no power-ups, then it's no longer possible to solve.
However, even if there is a block of metal, you need to make sure you can get it to the bottom row. You can apply the same logic as whether you can drop a diamond: if there are no blocks of stone (metal crushes stone), no gaps and no power-ups and the two isn't already on the bottom row then the puzzle is no longer possible.
This creates a chain reaction through the entire string of materials, although it gets a bit confusing by the time you get to ice.
Diamond Digger Tips #5: Know your power-ups
The power-ups add a lot of variety to the puzzles. All of the puzzles which contain power-ups have solutions that were designed to use the power-up, although in a couple of cases there are a couple of alternative solutions. Any power-up can be used to make a move stick, but each one has other uses.
TNT
TNT blows up a fair number of blocks, so will often drastically change the position in which the important blocks of the puzzle lie. However, sometimes, the only way to remove the diamond from the puzzle is by using the TNT and if this is the case, you need to get the diamond (or other important block) in the right place before blowing up the TNT to avoid the hole it creates being plugged.
Lava
Similar to the TNT, the lava also changes the playfield by a fair amount and activating one under a diamond may be the only way to remove the diamond from the board. However, because it creates a column of gaps, activating a lava will also normally allow you to do several other moves following its use.
Crumble
Some of the most difficult puzzles use this block. It will remove the bottom row of blocks, so people often use it to make progress, but it's often false progress as the rest of the layout remains the same. The only way to solve some puzzles with these in is to leave it until the very end and then activate it only when the diamond reaches the second row from the bottom.
Anti-crush
This power-up turns the logic of the game upon its head as when it's activated, any block can crush the block that it would normally be crushed by. However, it just means that you can use certain blocks to crush things that they normally wouldn't, giving you more options to solve the puzzle.
That wraps up the Diamond Digger tips, but here's a video of the full tutorial