Boktai (GBA)

Sol Emblem
Heal the Solar Tree enough that all the brances are filled, then talk to Lita.

Luna Emblem
Enter Asure Sky Tower with all other emblems.

Cloud Emblem
Randomly given to you the first time you enter the tower, if not received you must trade for it.

Dark Emblem
Complete the game once.

Earth Emblem
Randomly given to you the first time you enter the tower, if not received you must trade for it.

Flame Emblem
Randomly given to you the first time you enter the tower, if not received you must trade for it.

Frost Emblem
Randomly given to you the first time you enter the tower, if not received you must trade for it.

Infinite Solar bank energy
Go to the solar bank and deposit all your Sol there, then save and turn off the power, turn it back on and go to options, set the date to a few months/days (possibly years) forward, then load, go to the solar bank and your account will have grown to about 999, withdraw the sol and then you have near enough infinite sol in the solar station.

Sensitive Sensor
In the beginning of the game it tells you to cover your sensor, do this in an extremely dark place and then you will get more light.

Obtain Dark Gun Parts
Beat the game once to get the Dark Lens. Beat the same game twice to get the Dark Frame. Beat the same game again on hard mode to get the Dark Battery. You cannot mix the Dark parts with the normal parts. The Dark Gun can only function when all the Dark Gun parts are combined.

Black Hole Sun
To trick the solar sensor, you can use a black light in order to recharge your power.