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:
Kadru wished to have for sons a thousand snakes all of equal splendour. And Vinata wished to bring forth two sons surpassing the thousand offsprings of Kadru in strength, energy, size of body, and prowess.
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:
And seeing that the snakes had multiplied exceedingly, the Grandsire [Brahma], moved by kind consideration for his creatures, sanctioned with all the gods this curse of Kadru. Indeed, as the snakes were of virulent poison, great prowess and excess of strength, and ever bent on biting other creatures, their mother's conduct towards them -- those persecutors of all creatures -- was very proper for the good of all creatures.
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:
Adiseshan, the eldest son of Kadru, and the serpent that Vishnu reclines upon
Vasuki, the snake who was used as the rope to turn Mount Mandara in the Churning of the Ocean
Takshaka, the king of the Nagas I mentioned earlier who killed Arjuna's grandson Parikshit
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:
Lord Brahmā created the region below the earth for the demons and the Nāga snakes. In this way the destinations of the three worlds were arranged as the corresponding reactions for different kinds of work performed within the three modes of nature. [SB - 11.24.13]
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.