First, you need to free the two pets that you're able to (one is behind locked blocks)
Once these two are free (and only then) your very next move will bring down the key, so judge wisely where to make this move.
Unlock the board and work on getting Pets down as efficiently as possible.
Use the balloons to help create large groups of the one colour to help you.
Only two pets (maximum) are on your board at a time and some moves you only get one!
No more Pets will fall until you completely remove these.
When you have rescued ten of the pets, the game gets nasty...and drops viruses and random mesh machines!
Luckily there are also line blaster (springs) that fall now too.
It is better if you can plan your last few moves to just avoid these obstacles, but not always possible.
Remember, you can use the spreading viruses to your advantage to help clear the board.
Good luck, it's a tricky level!