Rockets clear all tiles in a row or a column depending on the direction they are pointed in. Match 4 pieces to get a rocket. 

Double tap Bomb or switch it with piece next to it to activate, it will remove significant number of pieces. Match five or six pieces in an L or T formation to get a bomb.

Boomerang removes one random piece on the field. It tends to hit locked elements or level goals first and destroys neighboring pieces while taking off. Match four pieces of the same type in a square to get a boomerang.

Pinwheel removes all the pieces of the same type from the field. Match five pieces in a line  or seven pieces in T formation to get a pinwheel.

Power up combinations

Rocket + Rocket clears the row and the column of that tile.

Rocket + Bomb clears three rows and three columns of that tile.

Bomb + Bomb clears the items within a four-tile radius.

Boomerang  + Bomb makes an explosive Boomerang that flies to random tile and explodes.

Boomerang + Rocket makes a Boomerang that carries a rocket to random tile and explodes.

Pinwheel + Rocket or Bomb or Boomerang makes the Pinwheel turn all the pieces of one type (the one currently the most common on the field) into respective power-ups.

Pinwheel + Pinwheel clears all the items on the board, and it also clears one layer from any obstacle.

Boomerang + Boomerang produces three Boomerangs that target different tiles.