Flushed Away

Hint: Rodney's weapon:
Go up to an enemy and keep pressing Triangle. This will kill them.
SJEZebra.

Hint: Roddy's sword:
After you complete the game and replay one of the levels before Arachne's Revenge, notice that Roddy has the toothpick. If you complete Arachne's Revenge and replay an earlier level, Roddy will have his sword again. It does no more damage than the tooth pick, and just looks fancy.
Danny Kriner.

Hint: Defeating Arachne:
To defeat Arachne (the first Boss), find the glowing pedal on the ground. Go to it and press Circle. When Arachne gets close, press Circle to throw the "egg". She will leave her stance to care for her egg. Follow and attack her. Do this as many times as needed (usually three or four) and she will disappear. Go through the new door to finish the level.
badtimdlrt.

Hint: Faster boat:
To make the Jammy Dodger boat go faster, either hold X and keep going straight, or continue moving while moving the Left Analog-stick Left and Right then straightening it out.