Defeating Vezon
After you defeat all Piraka, you will have to fight Vezon for the last time. First hit him the back, then in the legs, then the heads, then Vezon. After that you can play as Vezon in all levels.
Easy Lego Pieces
Completely upgrade Toa Nuparu at the Matoran Enclave shop. Collect 500,000 Lego pieces and buy 'Bonus Level 1'. Go to the Piraka Playground. Go to the other side of the playground. Once there you should find a cave/pathway between the Piraka VIP lounge and the Piraka diving board. Go inside the cave and there are three portals. Go through the first portal on your left. Once you are in, switch to Toa Nuparu and start destroying multiple enemies while collecting Lego pieces. Do this quickly, as you have a 112 second time limit. You can get an average of 50,000 to 70,000 pieces every time you try the bonus level.
Collect all the Lego bits in the Matoron Enclave then go to the Priaka Playground. Go back out. Keep doing this for a lot of Lego bits.
Defeating Guhhrahk...