And a little more detailed description about those stones-that-are-turning-to-5-gem type obstacles.

Check attached picture. On this stage (251) you have to collect 70 yellow gems to win (among others). But if you check the stage, you will see that there are no yellow gems on it (and if you clear level, yellow gems still not dropping, only green, red, pink and light blue).
You can get your needed yellow gems from destroying those stone type obstacle (see red arrows). Each obstacle when destroyed counts you as 5 gems. Funny part is, that when you destroy those obstacles, and get 5 yellow stone in your counter, it also can fill and light all yellow pets.

However I do not recommend to use those yellow pets (see on picture). Since - as I earlier said - when you fill Theo (as an example) you will not get any yellow bomb, coz there is no yellow gem on the table. However you can use Anubis, and benefit its "charges 1 lamp" bonus (note you will not get bomb).

Later I will explain how you can benefit from those obstacles when there are arrows on the stage.

Click image for larger version. 

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