The trick is to have precision in your aim, because you’ll have to do the major part of level 52 shooting via the walls. If you don’t want to or have had the opportunity to buy a charm of precision you just have to practise your aim. It helps to focus on a specific part in the wall, when you aim to shoot an angle. Don’t spend coins on Magic Potions before training this level a few times. I cleared the left side of the Skull Bubbles first and had a breeze after that. I used the background to adjust my aiming.
On the picture to the left I have circled what one might want to do, lift the bubbles a few rows (not too many, as you will waste bubbles if they go to high) that gives you more possible shots in the beginning of the game. You still have plenty of bubbles left to make a green spider or two after clearing out the devious Doom Bubbles first.
Video, 3 Stars. As you will see it gets easy when you have cleared the nether bunch of Doom Skulls.
Here is another good video that walks you through the level.
And, since this is such a hard level, here is a third one for the basic Strategy:
Here is two strategy pictures made by Arwen Elfe Gris and Hair’Oïne Coiffure. They shows how to aim both in the beginning and at the upper part of level 52
I wish all of you luck clearing level 52! :)