Level 15: Titan Mine
Enemies: Small Hulk, Medium Hulk, Super Hulk, Cloaked Hulk
This mine is guarded entirely by Hulks. I didn’t find it that difficult because the hulks are slow and bulky although there are a few Super Hulks to be careful of. From the starting position take out the Hulks. The Blue Door is down the tunnel to the right. The Hostages are around to the left.
The blue key is in a room behind a grate opposite the hostages. You’ll need to shoot the wall down and to the right of the door to open up a secret which leads to the Blue Access Key. Head back and go through the Blue Door. The Yellow Door is off to the left. There are 2 Robot Generators here but they only activate once you’ve destroyed the reactor. Go through the door on the other side of Yellow Door.
There’s an Invulnerability and 2 Shield Boosters in one of the alcoves. If you look up you’ll also notice the exit is here. Save the Invulnerability for the run to the yellow key or for taking out the core. The Red Door is also in this room and is guarded by a couple of Super Hulks.
Head through the door opposite the alcove and take out the Medium Hulks. Hunt around for a few secrets and then take the door to the left. The Yellow Access Key is at the end of this section. You can go back for the Invulnerability and make a dash for it and then come back or carefully take out all the Hulks and then pick up the key.
Make your way back to the Yellow Door, fly down and take out all the Medium Hulks. The Red Access Key is at the bottom, behind a grate and protected by two Super Hulks. You may want to use a Mega Bomb or Smart Bombs for this section. Pick up the key and head back to the Red Door.
Reactor Core: This is actually pretty easy. The Reactor is guarded by Super Hulks but you can shoot at them and the core from outside the red door. If a Super Hulk locks onto you just slide behind the corner.
Exit: Turn around and the exit is in the roof in the alcove that had the Invulnerability.