Are there any references to reptilian-like entities in Hinduism? Are they friend or foe, what kind of acts have they committed, etc.
The Nagas are a race of snake people mentioned throughout Hindu scripture. Their origin is described in the Adi Parva of the Mahabharata. The sage Kashyapa, son of Marichi the mind-born son of Brahma, had many wives, daughters of Brahma's son Daksha. Through them he had countless children, among them gods like Indra and other Adityas through Aditi, demons like Hiranyakashipu and other Daityas through Diti, etc. Now two of his wives were named Vinata and Kadru, and he offered them each a boon. This is what they asked for:
Those thousand snake sons of Kadru were the first Nagas. (By the way, Vinata's two sons were Surya's charioteer Aruna and Vishnu's bird vehicle Garuda.)
A lot of the Nagas were killed in a Yagna (fire ritual) carried out by Arjuna's great-grandson Janamejaya, to avenge the death of his father Parikshit at the hands the Naga king Takshaka. (Janamejaya was persuaded to stop before he killed them all, though.) But the ultimate reason they were killed is that they were cursed by their mother Kadru for disobeying them. And Brahma and the other gods allowed this curse to be enacted, because of how cruel the Naga race was to others:
So that answers your question about what they're generally like.
A later chapter in the Adi Parva mentions that there are "many thousands and millions" of Nagas, and gives the names of quite a few of them. But here are three of the most prominent Nagas:
There are lots of instances of snake people in Hindu texts. They are generally referred as Nagas. They live in the Nagaloka that is believed to be in Patala under the earth. They are just another kind of species created by Brahma:
So they are just another kind of species and hence neither inherently friends or foes to humans. But many references are there where their behaviors are friendly. Even marriages also have taken place. For example, Arjuna married Ullupi who was a Naga kanya. The epic Mahabharata mentions about the Nagas at many places.