System Defender is a tower defense-style mini-game that is playable in the EPF Command Room. It is set in the EPF Mainframe Computer where you have to defend it from threats.
The game has six levels to choose from:
|Level #||Briefing||Main Enemy||Stamp|
|1||Enemy bots are attacking the EPF mainframe computer. But who is responsible?||Enemy Bots (released by Rookie by accident)||Bug Overload|
|2||HERBERT ATTACKS! Herbert is set on destroying the EPF. Can you stop him in time?||Herbert P. Bear||Herbert Attacks|
|3||The EPF faces one of its toughest challenges when it's attacked by... Klutzy?||Klutzy||Klutzy Attack|
|4||The Test Bots are attacking all at once. Can you outsmart all three?||Test Bots||Test Bot Trio|
|5||RED ALERT! The Ultimate Protobot is attacking the EPF mainframe. Battle stations!||Ultimate Proto-Bot 10000||Protobot Attack|
|6||TRACK HERBERT! Herbert P Bear is back with more tricks up his sleeve. Are you ready to face him?||Herbert P. Bear||Track Herbert|
The red cannon shoots fast but has low damage. It costs 50 energy and is best used for the beginning of all levels.
The orange cannon has a long range but only moderate damage and firing speed. It costs 125 energy and is best used in places where red and purple cannons would not be able to hit bots.
The purple cannon does a considerable amount of damage, but fires slowly. It deals a fatal blow to each bot it hits. It costs 200 energy and is best used against Purple and Boss bots.
Gears are items used to upgrade cannons. They are sometimes dropped by boss bots, but they can be bought for 500 energy. When used on red cannons, they add more shots per hit. For orange cannons, they increase damage and range. For purple cannons, they increase damage and add mini shots, which do a fair amount of damage and are somewhat faster than the regular shot of the cannon.
- Red bots attack in large groups.
- Best suited cannon: Red, because they can deal damage over a large area by firing quickly.
- Orange bots are the fastest bots but have low health.
- Best suited cannon: Orange as it has a large range and can hit more bots.
- Purple bots can take lots of damage but are slow.
- Best suited cannon: Purple as its beam of energy is powerful and you don't need a high rate of fire.
At the beginning of the game, you have a starting amount of 200 energy. Sometimes enemies drop extra energy, which can range from 5 to 50.
- Red Cannon: 50
- Orange Cannon: 125
- Purple Cannon: 200
- Gear: 500
- Use the 200 energy at the start to place 4 red cannons, except for the "Tracking Herbert" level, where you should put up 1 purple cannon on a corner.
- U-turns and corners are the best places to put red cannons.
- Once most of the U-turns and corners are filled with red cannons, build orange cannons separated evenly by each other.
- Build multiple groups of orange cannons clustered in groups of 2-6. Orange cannons are extremely good at protecting against huge waves of bots.
- Build purple cannons when the bosses start appearing in huge groups. They are the perfect anti-boss weapons.
- When upgrading, upgrade one cannon fully before upgrading the next.
- Try to completely upgrade each cannon.
Some levels include Elite Medals as rewards — all include coins and stamps.
|Garbage Disposal||Destroy 100 enemies in 1 level|
|Bug Overload||Protect the EPF mainframe from rogue bugs|
|Strategic Success||Destroy 100 enemies without upgrading cannons|
|Mono Mechanic||Complete a game with only one type of cannon|
|Tactical Pro||Destroy 100 enemies without taking damage|
|Master Mechanic||Fill every open socket with a cannon|
|Herbert Attacks||Complete the level 'Herbert Attacks'|
|Klutzy Attack||Protect the EPF mainframe from Klutzy|
|Strategic Master||Destroy 250 enemies without upgrading|
|Tactical Ace||Destroy 250 enemies without taking damage|
|Test Bot Trio||Protect the EPF mainframe from the Test Bots|
|Protobot Attack||Protect the EPF mainframe from Ultimate Protobot|
|Track Herbert||Complete the level 'Track Herbert'|
- The Ready For Duty Stamp was removed from the game as of January 24, 2018. This was due to a glitch that made it unavailable to all players.
- The last Stamp Book polaroid of System Defender couldn't be seen until November 8, 2019. The required stamp amount for the last polaroid was reduced from 16 stamps to 13.
- The level briefing for level five is a reference to the "Red Alert!" line from the Star Trek franchise.
- System Defender used to be more difficult due to Club Penguin Rewritten running at a higher frame rate than Club Penguin, making it run faster than it should. This also affected Pizzatron 3000. It was still possible to complete, although extremely difficult. The frame rate was lowered on January 10, 2020.