I copied the link and pasted it but when I just now tried it it did not take me back there. You can also do a search of: Monster Busters: Hexa Blast (Paula Thorne) she has a lot of levels on YouTube but they are in numerical order so just scroll down to level 831.

I was stuck too and found your request then found this YouTube video by Paula Thorne. I have cleared this level now. One or more of the bubbled monsters have to make it to the top where the metal sliding thing is then since it is bubbled it will rise up and move the sliding thing out of the way and the shields will drop. Then you can wipe them all out. Hope you get all this info okay.

https://www.youtube.com/watch?v=uAjHyioNueQ