Do not think much about demons, spirits and the like. In reality, there are no gods and demons. A god is compassion and a demon is self-grasping. From self-grasping, the negative emotions arise, and they are the cause of all suffering, for others and yourself. This is the actual demon, there is no other demon apart from that. If you want to eliminate that demon, you have to cultivate love and compassion.
Ultimately, gods and demons are the same, as all beings have a single ground of mind. If from this mind temporarily self-grasping arises, you can label it a demon. It is very important to understand the levels of becoming a bodhisattva. For this, you must first understand the suffering nature of samsara. Everything in samsara has the nature of suffering, only when one realises the nature of mind, attains enlightenment, one will be free from suffering. If you want to be free from suffering, you must be free from self-grasping, as all suffering comes from wishing for one’s own happiness. The only way to be free from self-grasping is to cultivate compassion. This is the root of all happiness.
It is most important that you develop love for all beings. If you have cultivated love, you will have the power to overcome suffering. Even if you experience some temporary suffering circumstance, you will understand that this is the result of your own actions of self-grasping and you are now purifying this negative karma. If you now cultivate bodhicitta, you will not suffer again in the future. So if you experience some suffering now, you must understand that this is the result of your own actions, and is not caused by anyone else. If you understand this, you will accept your suffering and avoid negative actions to avoid future suffering.
For example, the cause of the hell realms is anger, the cause of the hungry spirit realm is greed, each of the six negative emotions is the seed for the six realms of samsara. If you find these seeds inside your mind, you must work hard to eliminate them each and every day through sustaining mindfulness. You must recognise the emotions upon arising and see its fault. Then, you must sustain mindfulness and not fall under the power of the emotion, not act out on it. Then gradually, the negative emotions will disappear. Always remember this. This is the root of all practice.
— Garchen Rinpoche