Parasite

Your patron is basically Venom. You and your DM can be as creative with this as you wish. You could have the parasite talk to you in your head, it could be like a voice that everyone can hear. It could be like a second head, whatever you can think of.

The Parasite Expanded Spell List

The Parasite Expanded Spells

Spell Level	Spells
1st	absorb elements, inflict wounds
2nd	alter self, enhance ability
3rd	animate dead, bestow curse
4th	dominate beast, polymorph
5th	contagion, dominate person

Regenerative Bond

Your patron will try its best to keep you alive by assisting in your death saving throws and purging your body of diseases. During death saves you add your charisma modifier to death saving throws(Minimum of +1) and you are immune to disease.

Parasitic Possession

As an action you can transfer your consciousness to another creature. In order to do so, the creature must be a humanoid or a beast(see controlling beasts), the same size or smaller as your original body, and have a CR equal to or lower than your level. You must be conscious to transfer into a new body. They must make a charisma saving throw contested with your spell save DC, if they fail then you gain control of their body for 1 minute. While in control of their body, both your body and their body are active which you control both of, you can only have control of 2 bodies at a time however. While in their body you have all the same stats as them except for your charisma, intelligence, and wisdom, but you also gain their initiative, and access to any of their current memories(2 weeks). You do know any languages that the new host knew but after the possession ends, you forget any languages you didn't already know. You also get to know every one of the new hosts stats. You do keep your languages, spells, class features, and feats while in their body. You can use either from either body but they share spell slots and feature uses. The possession requires concentration to maintain. If your original body drops to 0 hit points then their consciousness returns and you go unstable. When this feature ends, the target will return to consciousness but will not remember anything that happened during your time in their body. This feature can be used a number of times equal to your charisma modifier per long rest. The range of this feature is 60 ft. At level 12 you can also take control of humanoids that are one size category larger than you. 

Controlling Beasts                                                                                                                                                                                                                                                                                                          When controlling beasts, different rules apply then those of controlling a humanoid. The beast can additionally be one size category larger than your original body. The beast still makes a charisma saving throw but the DC is lowered to 10 as beasts are harder to understand and take control of. Beasts can be controlled in groups however. You are able to control of up to two beasts(swarms can not be taken control of). If you lose concentration then both possessions end. Spells, class features, and feats cannot be used in the beasts bodies. Although you still know all of your original languages, you are unable to speak anything the beasts couldn't already speak. Anything else is the same for possession. 

Parasitic Body

As an action you and your parasite will create a perfect bond allowing you and your parasite to become one. For 1 minute your maximum and current HP will increase by one half of your total HP. If your HP goes to 0 then this feature ends and you will instead be returned to 1 HP. This feature can be used 1 time before needing to take a long rest.

Complete Body Takeover

Just like using your Parasitic Possession, you can use an action to attempt to take control of a new body, however if they fail their save by 5 or more, are a humanoid, and are under 100 health, then you take complete control over their body permanently. If you do not wish to abandon your body you can instead choose to do a normal use of Parasitic Adaption.  When you take full control of a body, your old body will disintegrate leaving all of your possessions. Your new body will maintain all your previous languages, class features, feats, spells, charisma, intelligence, and wisdom scores. You will lose any racial features you previously had unless the new body is the same race. This feature can be used 1 time every day.  At 20th level, this feature can be used as a free action after failing 3 death saves. If the target fails your Complete Body Takeover DC then you gain full control over their body and are saved from the brink of death. You will be at 1 quarter of your new bodies max HP regardless of their actual health after this.

Your new body will begin to regain it's lost stats and abilities after 1d4 days of light activity. After the days pass, your new body will change to look exactly as your original body did, unless you choose to keep the looks of the new body. If you do choose to keep the new bodies looks and it is a different race than your original body, you will not regain any racial features from your original body and will instead gain the new bodies racial features.