His Desire Manipulation allows him to change what someone 'desires', and to what extent. For example, he could increase something passive, such as a 'desire' to clean your room, or something malevolent, such as a 'desire' to throw yourself into traffic.
The venom created by Feel Good Inc. is primarily composed of morphine, sending its victims into a numb, happy daze. Large doses of this venom can potentially kill the victim.
Feel Good Inc. is a tall, red and white humanoid alien with pink hearts on his chest and legs. He has a semi-robotic appearance, with strange white tubing making up his middle abdomen, glassy eyes, and having his arms on some sort of swivel. The StarTrix Requiem symbol is on his abdomen.
Those with sufficient willpower may be able to resist the 'desires' FGI induces. In addition, the poison he generates is unable to soak through metal or glass of any kind.