You can choose between 2 power-ups in this game: The hammer, this will hammer away a few blocks making room to place new blocks. And the bomb, when you use the bomb it will destroy a piece of the field, removing all pieces around it.
A good strategy to connect multiple animals is by sharing the blocks they can walk over. There is no need to make 3 paths if there are 3 animals. Just make 1 path and connect the last bits to all the different animals. The same counts for the keys, you can share the roads.