魔 means “evil” or “demon”, and a noun with the particle の modifies the following noun 神 meaning “god” so 魔の神 means “god of demon” or “demon god”.
The combination of the particles と and やら is used with something you vaguely remember, or you’re not familiar with. So when it’s used with someone’s name, it means you’re not really sure of the name but don’t bother asking. Therefore, it often sounds rude if you use this when calling someone’s name.
So 魔の神とやら can be translated as “Demon God or whatever it’s called”.
人間 (noun) means “human”.
“Someone に a verb passive-form” means “to be done something by someone”. 見下される is the passive form of 見下す meaning “to look down upon” so 人間に見下される means “to be looked down upon by a human”, and it modifies the following noun, 気分 meaning “feeling”.
は is the topic particle. So the topic of this sentence is 人間に見下される気分 which directly means “feeling of being looked down upon by a human”.
どうだ is the combination of the interrogative どう meaning “how” and the auxiliary verb だ. だ is usually used with a noun or na-adjective when you want to assert or declare the statement such as こっちだ meaning “It’s this way!” 明日は雨だ meaning “It’s going to rain tomorrow”. But when it’s used with interrogative words like だれ (who), どこ (where), いつ (when) and so on, it expresses the speaker’s strong demand for the answer. So it’s often used by a very manly or bossy person.
So 人間に見下される気分はどうだ directly means “how is the feeling of being looked down upon by a human“.