Demon Summoner

You start with a device called a COMP which is shaped like an item/weapon of your choice, and is what allows you to forge contracts and summon creature to aid you in battle.

You can make a contract with any creature of a type listed later (provided the creature meets the limitations stated later on). it's up to the DM to decide what they want in order to make a contract(example would be 50-300 gold or 10 points of HP). 

You can summon a number of creatures equal to your proficiency bonus per long rest. you can have a number of contracts equal to your CHA SCORE. Your summoned creature stays until it dies or you un-summon it. if it dies you can't summon it again for 3 days.

COMP

A COMP can be any item, though usually it's a kind of weapon, from a gun/crossbow to a longsword. it does the damage of said weapon it takes the form of. A COMP is what allows you to make contracts and then summon creatures in battle. A COMP gives +1 AC when equipped. You can use your CHA mod instead of STR/DEX when making attacks with a COMP.

You can't summon creatures or cast magic without a COMP.

The summoned creature takes its turn right after yours and you control what it does. 

You can make a contract with any Aberration, Celestial, Elemental, Fey, Fiend, or Undead, that is CR 1/2 your total level(rounded down).

Having a creature summoned gives +2 AC to you.

Enhanced bond

The bond between you and your summons have increased.

Your summons can now cast one spell you know without expending one of your spell slots. (the spells LVL can not exceed half the creatures CR rounded down) 

Sacrifice

You can sacrifice a summon to gain their remaining HP as your own in temporary HP.

Dual summon

You may now have two creatures summoned at the same time.