The problem with multiple gem explosions is that they do NOT overlap.
Let’s take as an example TimeKnight’s 3x3 gem block. If you duplicate it, and have 2 gem blocks next to each other, and explode the middle blue on first block, and the skull on the second block. It will not remove 18 gems.
The first explosion, the middle blue, removed the whole first block. The secone explosion, the skull, removes the skull and the 3 connecting gems. So 13 gems removed, instead of 18.
So if you have troops like TDS, that explodes 9 random gems, the actual ammount of gems removed is wildly variable. Sometimes you can clear the whole board with his 9 explodes. Sometimes you can clear like 17 gems. And the mana gain follows the randomness ofc.