Praise be to Allah.

Firstly: 

Most scholars are of the view that it is not possible for any human – except the Prophet (blessings and peace of Allah be upon him) and his fellow Prophets – to see the jinn in their original form, which is not known in the first place. So any statement with certainty that they take a particular form is not something to be believed without question. Those who say that it is not possible to see them in their true form quote as evidence the verse in which Allah, may He be exalted, says (interpretation of the meaning):

“Verily, he [Shaytaan] and Qabeeluhu (his soldiers from the jinns or his tribe) see you from where you cannot see them”

[al-A‘raaf 7:27]. 

Ash-Shaafa‘i (may Allah have mercy on him) said: 

If a person who is of good character claims that he sees the jinn, his testimony becomes invalid because Allah, may He be glorified and exalted, says (interpretation of the meaning): “Verily, he [Shaytaan] and Qabeeluhu (his soldiers from the jinns or his tribe) see you from where you cannot see them”[al-A ‘raaf 7:27] – unless the person who says that is a Prophet. 

See: Ahkaam al-Qur’an (2/195, 196) by al-Qurtubi 

Ibn Hazm (may Allah have mercy on him) said: 

The jinn are real, and they are part of the creation of Allah, may He be glorified and exalted. There are disbelievers and believers among them; they can see us but we cannot see them.

Al-Muhalla (1/34) 

This does not contradict what has been proven of seeing them in the forms of humans or animals; the inability to see them is only applicable to seeing them in their real form. 

Al-Haafiz Ibn Hajar (may Allah have mercy on him) said: 

He – i.e., the Shaytaan – may appear in different forms that can be seen. The words of Allah, may He be exalted, “Verily, he [Shaytaan] and Qabeeluhu (his soldiers from the jinns or his tribe) see you from where you cannot see them”[al-A‘raaf 7:27] – apply only to seeing him in the form in which Allah created him.

Fath al-Baari (4/489) 

Secondly: 

Allah, may He be exalted, has given the jinn the ability to appear in the form of humans and animals; there is sound evidence to that effect and that is known from real events. 

It was narrated that Abu Sa‘eed al-Khudri (may Allah be pleased with him) said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “In Madinah there are some of the jinn who have become Muslim. Whoever sees any sign of these inhabitants, let him warn him for three days, then if he appears after that let him kill him, for he is a devil.” 

The word translated above as inhabitants refers to snakes that may live in houses. 

The Shaytaan came in human form to Abu Hurayrah, claiming to be poor and in need; the hadeeth will be quoted below. 

It was also narrated that he appeared in the form of Suraaqah ibn Maalik. 

Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: 

The jinn may appear in human or animal form; they may appear in the form of snakes, scorpions and so on; or in the form of camels, cattle, sheep, horses, mules and donkeys; or in the form of birds. They may also appear in human form, as the Shaytaan came to Quraysh in the form of Suraaqah ibn Maalik ibn Ja‘sham, when they wanted to go out to Badr. Allah, may He be exalted, says (interpretation of the meaning):

“And (remember) when Shaitan (Satan) made their (evil) deeds seem fair to them and said, ‘No one of mankind can overcome you this Day (of the battle of Badr) and verily, I am your neighbour (for each and every help).’ But when the two forces came in sight of each other, he ran away and said ‘Verily, I have nothing to do with you. Verily! I see what you see not. Verily! I fear Allah for Allah is Severe in punishment’”

[al-Anfaal 8:48].

Majmoo‘ al-Fataawa (19/44, 45) 

He (may Allah have mercy on him) also said: 

The black dog is the devil among dogs, and the jinn often appear in that form, and also in the form of black cats, because the black colour is more able to concentrate devilish power than other colours, and it concentrates heat.

Majmoo‘ al-Fataawa (19/52) 

Dr. ‘Umar al-Ashqar (may Allah have mercy on him) said: 

Sometimes the devils come to man not by way of waswasah (whispering insinuating thoughts); rather they appear to him in human form, or a person may hear a voice and not see a body. Or they may appear in strange forms, which come to people and tell them that they are from the jinn. Sometimes they lie and say that they are angels, and sometimes they call themselves “men of the unseen”, or claim that they are from the spirit world. In all cases, they speak to some people directly, or by means of one person who is called a “medium”, whom they possess and they speak on his lips. Or the response may come in the form of writing, or it may go further than that and they may pick a person up and fly with him through the air, and transport him from one place to another. Or they may bring him things that he asks for. But they only do that to those who are misguided and who disbelieve in Allah, the Lord of heaven and earth, or who do evil deeds and things that incur divine wrath. Those people may pretend to be righteous and pious, but in fact they are among the most misguided and evil of people. The earlier and later generations have told many stories about this matter, to such an extent that it is not possible to reject or deny them, because they have been narrated by so many from so many.

‘Aalam al-Jinn wa ash-Shayaateen (p. 115) 

Thirdly: 

There is no difference between the month of Ramadan and other months with regard to seeing the jinn in different forms; rather it is proven in a saheeh hadeeth that the jinn may appear in human form during the month of Ramadan. 

It was narrated that Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) put me in charge of guarding the zakah (charity) of Ramadan. Someone came to me and started scooping up handfuls of the food. I grabbed him and said, ‘I will take you to the Messenger of Allah (peace and blessings of Allah be upon him).’. He said: ‘Verily I am in need, and I have dependents and am in great need.’ So I let him go. The next day, the Prophet (blessings and peace of Allah be upon him) asked me: ‘O Abu Hurayrah, what did your prisoner do last night?’ I said: ‘O Messenger of Allah, he complained of great need and having dependents, so I took pity on him and let him go.’ He said: ‘He lied to you and he will come back.’ Then I knew that he would come back, because the Messenger of Allah (blessings and peace of Allah be upon him) said that he would come back. So I lay in wait for him, and he came and started scooping up handfuls of the food. I grabbed him and said, ‘I will take you to the Messenger of Allah (peace and blessings of Allah be upon him).’. He said: ‘Let go of me, for I am in need, and I have dependents; I will not come back.’ I took pity on him and let him go, then the next morning the Messenger of Allah (blessings and peace of Allah be upon him) asked me: ‘O Abu Hurayrah, what did your prisoner do last night?’ I said: ‘O Messenger of Allah, he complained of great need and dependents, so I took pity on him and let him go.’ He said: ‘He lied to you and he will come back.’ So I lay in wait for him on the third night, and he came and started scooping up handfuls of the food. I took hold of him and said, ‘I will take you to the Messenger of Allah, and this is the last of three times. You say that you will not come back, but then you come back.’ He said: ‘Let go of me, and I will teach you some words by means of which Allah will benefit you.’ I said, ‘What are they?’ He said, ‘When you go to your bed, recite Aayat al-Kursiy, “Allah! La ilaha illa Huwa (none has the right to be worshipped but He), Al-Hayyul-Qayyoom (the Ever Living, the One Who sustains and protects all that exists)…” [2:255] – until you complete the verse, for then you will have a protector from Allah and no devil will come near you until morning.’ So I let him go, and the next morning the Messenger of Allah (peace and blessings of Allah be upon him) asked me, ‘What did your prisoner do last night?’ I said, ‘O Messenger of Allah, he claimed that he would teach me some words by means of which Allah would benefit me, so I let him go.’ He said: ‘What were they?’ I said: ‘He said to me: “When you go to your bed, recite Aayat al-Kursiy from beginning to end, ‘Allah! La ilaha illa Huwa (none has the right to be worshipped but He), Al-Hayyul-Qayyoom (the Ever Living, the One Who sustains and protects all that exists)…’” And he said to me: “You will have a protector from Allah and no devil will come near you until morning.” – And they (the Sahaabah) were very eager to learn good things – The Prophet (peace and blessings of Allah be upon him) said, ‘Indeed he told you the truth, although he is an inveterate liar. Do you know who you have been speaking to for the last three nights, O Abu Hurayrah?’ I said: ‘No.’ He said: ‘That was the Shaytaan.’ 

Narrated by al-Bukhaari (3101) in a mu‘allaq report; an-Nasaa’i in ‘Aml al-Yawm wa al-Laylah (p. 533) 

This hadeeth indicates that it is possible for the jinn to change their form, and also that they may appear in Ramadan. The correct view is that those who are chained up during the month of Ramadan are the most rebellious devils (maarid), not all of the jinn.