History of the the Ancient Gods - Devils and Demons, elementals

The ancient gods have been locked away in hell, and are looked after by Hades (he pulled the short straw), and was appointed by the gods. He not only looks after the dead but manages the keys and access, being the jailor
There are ways of breaking through into this jail and letting out the main Demons/Devils, who desperately want to get out of their hellscape and get back to expanding their power base on the mortal plane. They have conspired with there followers and cultists to find ways to break down the prison or out of it (but would ideally like to move between all planes as they used to).
They have many plots including such escapades to steal the hammer of the underworld, kidnap Hades nymph, or sacrafice various people or special individuals.
They currently have cultists plotting ways to free there Gods, including

• Cults normally linked to the power of 13, (just so you are aware - there is the ability to expand the power of spells if you have the right "numbers" and symbols, and godly support.... 
• needing sacrifices lots of people, virgins, babies etc,
• Sacrafice and/or the power of special blessed, powerful or individuals with some God/angelic/demonic blood line.
• Powerful artifacts (such as the mother pearl/Hammer of the Underworld)

Equally powertfull individuals could break down the prison by opening the doors/gates and weaking the spells protecting the world from their presence
Therefore summoning any demon/God etc could have the following negative impacts

1. 6HD to 10HD = summoning, on a 1 - a critical failure, on the roll for spell cast, there is then a chance something bad happens,

• 1 - 50% another low level demon/devil/elementals arrives
• 51 - 75% 1d6 of baddie demons arrive
• 76 - 95% 2d6 demons arrive
• 96 to 99% a larger demon/devil with devil and demon guards
• 100% is oh shit - who has come through, and a 1% (i.e. 01 on 1d100) and the wall is broken and all hell is let loose - quite literally

Baddie groups trying to summon include;

1. Yuan Ti summoning Set - Thoth Amon is the evil Arch fiend here
2. Lolth and the Dark Elves
3. Demogorgon and his cult...(Priests of Justice) (Arendagrost - Lord Kagoth - succubus queen Malcanthet, Balor demon Belaphoss, Qill half elf cultist
4. Orcus
5. Elros
6. The Master - currently a Balgura demon...
7. Moloch - vrery few followers, except some older followers cambion related
8. Gorthir the half demon/troll
9. Sarn Durgba, is trying to summon demons/devils to assist him his quest against Elros the humans

Others....

1. Baphomet
2. Fraz
3. Grazzt
4. Jubilex
5. Yeenoghu
6. Tiamat
7. Zuggtmoy
8. Bael
9. Geryon
10. Hutijin
11. Titivulus
12. Zariel
13. Asmodeus