This is a solution for the Barbarian
class, but it should work for all classes that can create gems... just replace enrage and needed gems with the skill for your class.
1. create a quick game.
2. choose king godd.
3. save enough red, blue und yellow gems to use enrage 3 or more times.
4. use enrage und hope many red pearls stays in the match.
5. match 8 gems of the same color
king godd is very slow and give you enough time to do the combo, especially with all the extra turns from the x 4 combo. i got the x8 combo after 15 minutes and right before the x8 combo, i saw many red pearls survived on my 8x8 board... most of the times the small combos let most of your red pearls disappear... with a bit luck, many of them don't match and give you a much better chance for the next time you use enrage.
btw i didn't destroyed the 4 blocks, because maybe they fill slots and make the board even smaller and give a higher chance to let appear red pearls above the 2x2 block, but i never counted the created pearls, so this is just a theory, not a confirmed fact.
if you use enrage many times during the main story, maybe you have enough luck to unlock this achievement without boosting... i used enrage until level 40, but never had the luck to unlock this in a match (i only managed it to match 7 gems many times)... so i decided to try it this way and it should also work for you - with a bit patience.