Spider-Man: Friend or Foe Codes -

Unlock Venom and new Green Goblin
Venom and new Green Goblin (from the movie) can be unlocked by entering the following codes using the D-Pad when standing in the Helicarrier in between levels. You should hear a tone indicating you entered the code correctly and they will then be selectable from the sidekick select console:

, , , , , - New Green Goblin
, , , , , - Venom

Unlock Sidekicks
To unlock sidekicks, you have to either get to a certain point in the game or buy them from the shop:

Black Cat - Beat the tutorial level
Blade - Buy for 1000 tokens in the shop
Doctor Octopus - Buy for 500 tokens in the shop
Green Goblin - Buy for 750 tokens in the shop
Sandman - Buy for 1250 tokens in the shop
Venom - Buy for 1500 tokens in the shop

Achievements
Complete each achievement to get the allotted gamerscore:

All Tied Up (75) - Fully upgrade Web Stun with all available Abilities and Mods.
Arachnid Artillery (75) - Fully upgrade Web Shoot with all available Abilities and Mods.
Combo Meter Master (25) - Fill the Combo Meter all the way to Level 4.
Egypt Complete (125) - Find all collectibles, find all secrets, and defeat all bosses in this location.
Fury's Fourteen (75) - All characters are fully upgraded with all Attacks and Attributes.
Lightning Strikes (25) - Obtain a Hit Chain higher than 15.
Nepal Complete (125) - Find all collectibles, find all secrets, and defeat all bosses in this location.
Our Powers Combined (25) - Initiate a Hero Strike Power-Up.
Tangaroa Island Complete (125) - Find all collectibles, find all secrets, and defeat all bosses in this location.
Tokyo Complete (125) - Find all collectibles, find all secrets, and defeat all bosses in this location.
Transylvania Complete (125) - Find all collectibles, find all secrets, and defeat all bosses in this location.
Web Slinger (75) - Fully upgrade Web Line with all available Modifications.