Introduction to Vetalas:
It has been a trend since ancient times to do the siddhi of upadevatas like yaksha, kinnar, gandharva, vidhyadhar, vetal, siddha etc.. to make one's life materially safe and sound which inturn will make a solid base for spiritual journey. In the same series of upadevatas, Vetalas are energy beings belonging to the shaiva class of upadevatas. The first vetal was born from the union of Veerabhadra and his consort 'Krutya- Bhadrakali'. This vetal was known as 'Veer vetal'. He played a pivotal role in daksha yadnya vidhwamsa. He was worshipped as guardian deity then on because of his valour, strength and magical powers. From the first vetal the vetal family tree grew and they came to be known as a seperate yoni. These are one of the high ranking ganas of Rudra. They stand on a very elevated position in the hierarchy of the ganas. Amongst the extra terrestrial beings of nether realms there's a hierarchy established according to their powers which in ascending order is as follows: 
Bhoota, preta, pishacha, yaksha, shaka, daka, rakshasa, daitya, daanava, naaga,  bramharakshasa/ vetal, veer, kshetrapal, bhairav, Mahaveer.
As we can clearly see vetalas are ranked very high. They're equivalent to bramharakshasas in power. The difference between vetala and bramharakshasa yoni is the nature of people occupying that yoni and the type of karma which pushes them into these bhoga yonis. A bramharakshasa is a bramhan accomplished with the knowledge from chaturvedas, puranas,Upanishads etc.. and having occult  siddhis; but following adharma throughout his life and not giving his knowledge to eligible people. Whereas a vetal is a tantrik walking on Shiva-Shakti marga having equivalent knowledge and siddhis to that of a bramharakshasa but wastes his lifetime in chasing mundane goals. Also he/ she may be a yogabhrashta sadhak/ sadhika who couldn't complete their smashan/ vamachar/ aghora-yogic sadhanas. These may also be the high level mantravadi/ tantravadis who spoil other's life for petty gains. This is how the two yonis are occupied.
Vetalas are usually punished with solitude, hunger, thirst, in some caves, rivers, old banyan/pipal trees, mountain tops, dense forests and charnel grounds. Therefore these are the places where people can easily afflicted/ possessed by vetal entity or can go and do it's siddhi. Vetalas have a very long life. Somewhere between 1000-10,000 years. The time for them also runs slower as compared to a human being. There are Male, female and child Vetalas. Females are called as 'Vetalinis'. The vetala yoni is classified into 52 types of vetalas. These names have been extremely secretive till date but for our reader's knowledge we are publicising them. To avoid plagiarism few names are being omitted. The names of 52 types of vetalas are as follows:
52 Vetālas/betālas:
1 vīra betāla , 
2 mahābetāla,
3 agni betāla,
4 gagana betāla,
5 bhūmi betāla(bhū betāla),
6 jala betāla, 
7 pavana betāla,
8 mahāvīra betāla,
9 rājya betāla,
10 jaya betāla,
11 brahma betāla,
12 hanumān betāla,
13 guhiyā betāla,
14 dhana betāla,
15 rākṣasa betāla,
16 karṇa betāla,
17 śiva betāla,
18 trinetra betāla,
19 ghaṭaka betāla,
20 citeśvara betāla,
21 kapālī betāla,
22 ghaṃṭākarṇa betāla,
23 rūdra betāla,
24 budha betāla, 
25 ājñā betāla,
26 jalayāna betāla,
27 kālī betāla,
28 māraṇa betāla,
29 aichika betāla,
30 āgama betāla,
31 aghora betāla
32 ghāṃṭalā betāla,
33 ghaṭaka betāla,
34 pracaṇḍa betāla, 
35 bhoṃdā betāla, 
36 tāla betāla
37 jogiyā betāla
38 pītama betāla
39 śmaśāna betāla
40 rākṣasa betāla
41 ...
42 ....
43 ...
44 ...
45 ...
46 ...
47 ...
48 ...
49 ...
50 ...
51 haṃḍiyā betāla
52 paṃcatatva betāla
Amongst these 16 are satvik in nature, 11 are rajasic and remaining are tamasik. So when one invokes them, they should know the type of vetal and perform the rituals accordingly to get the best results.
Benefits of vetal siddhi:
Vetalas are beings primarily known for their magic, occult powers, illusionary skills, higher spiritual knowledge, might, valour and loyalty. Vetalas are usually very aggressive, fearsome and huge. But when one accomplishes them through sadhana they appear in a gentle form. They possess many knowledge treasures. One who successfully does vetal siddhi gets the following benefits: 
- magical powers like vaak siddhi, bhoota-bhavishya-vartaman darshan siddhi, aakasha gaman siddhi, jala gaman siddhi, sammohan Shakti, rahasya dnyaan siddhi, shunya siddhi etc..
- vetal sadhana also gives mighty strength into one's body and mind this making them physically strong, courageous and mentally genius.
- vetal are well versed in various tantras too, hence they also give the indepth and secretive knowledge of different occult sciences like jyotish, vanaspati and aushadhi vidnyaan, alchemy or kimiyagari, rasa vidnyaan, bhu garbha siddhi, many tantra practices of itar yonis, devata siddhi patalas, yoga siddhis etc..
- they're excellent protectors and can safeguard their master in all the conditions. They can protect from accidents, misfortunes, diseases, natural calamities, black magic, spirit attacks, evil eye, enemy attacks etc..
- vetalas are usually accomplished in the form of 'bhrutya' i.e. a servant. Therefore they always remain in front of their master either in physical form or subtle form and carry out the instructions given by them.
- they can accomplish their master's wishes by going to any extent. They can even finish off the enemy clan. 
- vetalas are known for physically moving things from one place to another irrespective of the distance between two places and interdimensional phenomenon.
- they make their master into such a personality that all the man and women get Bewitched by their very presence and succumb to them. A vetal sadhaka has magnetic personality and knows no fear.
- vetalas can open the ways to the wealth in one's life in all four directions. Their sadhak never falls I'll and lives a long and happy life.
These were some of the benefits of vetal siddhi. There are many more, which one discovers after the siddhi with practical use. 
Brief history of vetal worship:
Most famous sadhaka of vetal in the history was the king of Ujjain 'Vikramaditya'. Who got his power, siddhis and accomplishments because of the grace and directions from the old vetal who's siddhi he did. Vetal upasana has been in key positions in Nepal, Kerala and Dravidian tantrik systems and in Konkan- Goa regions where ancient vetal murtis are discovered recently. Many of the Konkani GSB community people have vetal as their kuladevata along with a goddess. In natha tradition guru gorakhnath and kanifnath were exalted siddhas of vetal. They would make use of them to fly, deliver food, clothing and other necessities in jungles and also show magic to attract the masses.
Vetal sadhana details:
-  Vetal sadhana is started usually from amavasya, eclipses Holi, diwali, navratri, Vijayadashami. 
-  their sadhana is usually done in charnel grounds, on a hillock, in dense forests, in caves or on a river bank. Some of the saumya vetal sadhanas can be performed in one's home too.
-  vetal sadhana can  be done in satvik, rajasik and tamasik way.
-  it's a nishachari sadhana i.e. the one to be performed in night.
-  sadhak has to be Veera or fearless in nature.
-  this sadhana can be done by males and females both.
-  sadhana usually requires vetal siddhi yantra, black agate rosary/ rudraksha rosary/ bone rosary, powerful smashan Bhairav raksha kavach, water, panchapatras, rice flour, vermilion, kumkum, rice grains, incense, mustard oil lamp, red hibiscus flowers, peetha, red/ black cloth, red/ black clothes to wear, black turmeric, food offering depending upon satvik/ rajasik/ tamasik sadhana (honey & coconut water mixture, cooked rice & halwa-poori/ domestic alcohol, roasted fish, cooked goat meat or chicken/ raw goat or rooster liver, domestic alcohol, roasted fish).
-  there are two methods