Here's some types of proxies that you might become...
People who aren't proxies
Blind – People who have never heard or seen anything about the Slender Man. The closer definition is a bit blurry, since some would only use this for people who don’t even know the meme, while sometimes this term also includes people who have heard about Slender Man, but are not stalked by Him. First read on Walking the Hallowed Halls.
Fighters – Although they often have to escape Slender Man too, Fighters have a more active take on their problem. They try to find ways of defeating Slender Man, often activeley eliminating His human servants and allies on the way. Instead of outright killing, some Fighters try to find ways of rescuing the proxies and agents, and of gathering information about Slender Man they give to other Fighters. But they all struggle against Him. I’m not sure where this term first appeared, but It could be The Tutorial, White Elephants or Seeking Truth.
Runners – If not mentioned in another context, a Runner is a person who survived the first assaults of Slender Man or managed to flee in time. Runners are still haunted by Slender Man, but they learn how to escape Him properly to survive. Established by The Tutorial.
Stalked – I honestly do not quite know if this term is really an established one, but I heard it sometimes referring to people who have contact with Slender Man, but are not dead yet. Read: Runners and Fighters. I don’t know where I have it from.
Victims – Also a kind of blurry term. It refers to people who have had problems with the Slender Man, but is more commonly used for those who have already died or vanished. Some also use it as a term for Runners and Fighters. A common term with unknown source.
The Proxies
Agents – A term for people being on the side of Slender Man. It’s definition can range from people who do it out of free will to those whose minds already are deranged and manipulated by Him. Since other terms have been established too, it’s increasingly used for people who serve Him more or less out of their free will, be it due to fascination or blackmail. Those Agents are completely sane. First fully explained by Reach in a comment on White Elephants.
Berserkers – People who are under Slender Mans control, but do not depend on it to do something. They can still decide things on their own and if He gives them an order, they can do anything He does not forbid them to fulfill it. Thus while they’re already quite mad and fanatic, they’re still sane enough to be dangerous. Also first explained by Reach.
Hallowed/Hollowed – While the term Hallowed seems to be the first one to have popped up, due to it’s delicate implications Hollowed is more commonly used now between White Pawns, while Black Pawns tend to use Hallowed. The term refers to people who have been carved out by their contact with the Slender Man, which more or less erased all of their own personality to make way for an almost zombie-like obedient servant. If they don’t act like a much better disguised and quicker version of zombies, they show a fanatic obsession to Slender Man akin to religious fanaticism. They often communicate through codes and cryptic messages, sometimes having their personality post-Slender Man shining through. It’s worth noticing that they are said to be unable to do even the simplest things necessary to stay alive when they are not on a mission for Him. Again: First explanation by Reach, while the term was probably first featured at all in The Tutorial.
Proxies/Slenderproxies – Another term for Black Pawns, but more often than not referring to everything but Agents/Servants. Source unknown to me.
Revenants – A kind of Proxy mostly known about in rumours. They are said to have risen in the hierarchy enough to obtain own powers akin to that of Slender Man, albeit not as strong as His. There are very few of them and since they are less expendable than other Proxies it is rather unlikely for a White Pawn to come in conflict with one of them. Instead they seem to be used for organisation purposes. Their sanity seems to range between the status of an Agent and a Berserker, since they are clearly able to use their Free Time however they want, but also bend to the will of Slender Man. Mentioned by Reach, too – who stated that he was one of them.
Servants – A more recent term for Agents. First mentioned on Walking the Hallowed Halls.
Sleepers – People who are under control by Slender Man, but are not aware of that. They lead an usual life for most of the time and can never remember what they did under Slender Mans influence.While in Proxy mode, they act the closest to Hollowed, but can range to the sanity degree of Berserkers at least. Some White Pawns may actually (or also) be Sleepers. Also explained by Reach.
Taken – A more recent and neutral term for Hollowed and maybe Berserkers. While Hollowed may also refer to people being able to make very weak efforts on surviving, Taken rather describes Hollowed really unable to do anything not necessary not carry out an order by Slender Man. While Hollowed is used mostly by White Pawns who only see their behavior in mission mode, insider Andrew from Walking the Hallowed Halls raised this term in describing them from the point of view of an Agent/Servant. This is why I’ll mention separately here that they are described as being thoroughly mad, only using their codenames for each other, obsessed with masks and stalking people. Andrew also mentioned something like possibly telepathic communication [Andy Note: think "hivemind"] between them, since they have been seen interacting with each other without exchanging words while clearly showing signs of conversation. Servants obviously are not able to take part in the mental communication between them, possibly due to “too much” sanity.
Touched – Another term introduced by Walking the Hallowed Halls. It can be used as another word for Proxy, but most often it’s definition ranges from Sleepers over Revenants to Berserkers. Some Agents/Servants too have chosen to be what they are because they are – albeit in a weaker form – Touched. Basically the term refers to having had close contact with Slender Man, used by Him to transfer sensations to the human being which are not fit for the human mind or oppressing their will with His own for a while. Being mentally touched by Him this way sooner or later is said to lead into insanity, although Slender Man seems to have a certain amount of control over how long it takes to transform a person from a Touched into a Taken.
People who aren't proxies
Blind – People who have never heard or seen anything about the Slender Man. The closer definition is a bit blurry, since some would only use this for people who don’t even know the meme, while sometimes this term also includes people who have heard about Slender Man, but are not stalked by Him. First read on Walking the Hallowed Halls.
Fighters – Although they often have to escape Slender Man too, Fighters have a more active take on their problem. They try to find ways of defeating Slender Man, often activeley eliminating His human servants and allies on the way. Instead of outright killing, some Fighters try to find ways of rescuing the proxies and agents, and of gathering information about Slender Man they give to other Fighters. But they all struggle against Him. I’m not sure where this term first appeared, but It could be The Tutorial, White Elephants or Seeking Truth.
Runners – If not mentioned in another context, a Runner is a person who survived the first assaults of Slender Man or managed to flee in time. Runners are still haunted by Slender Man, but they learn how to escape Him properly to survive. Established by The Tutorial.
Stalked – I honestly do not quite know if this term is really an established one, but I heard it sometimes referring to people who have contact with Slender Man, but are not dead yet. Read: Runners and Fighters. I don’t know where I have it from.
Victims – Also a kind of blurry term. It refers to people who have had problems with the Slender Man, but is more commonly used for those who have already died or vanished. Some also use it as a term for Runners and Fighters. A common term with unknown source.
The Proxies
Agents – A term for people being on the side of Slender Man. It’s definition can range from people who do it out of free will to those whose minds already are deranged and manipulated by Him. Since other terms have been established too, it’s increasingly used for people who serve Him more or less out of their free will, be it due to fascination or blackmail. Those Agents are completely sane. First fully explained by Reach in a comment on White Elephants.
Berserkers – People who are under Slender Mans control, but do not depend on it to do something. They can still decide things on their own and if He gives them an order, they can do anything He does not forbid them to fulfill it. Thus while they’re already quite mad and fanatic, they’re still sane enough to be dangerous. Also first explained by Reach.
Hallowed/Hollowed – While the term Hallowed seems to be the first one to have popped up, due to it’s delicate implications Hollowed is more commonly used now between White Pawns, while Black Pawns tend to use Hallowed. The term refers to people who have been carved out by their contact with the Slender Man, which more or less erased all of their own personality to make way for an almost zombie-like obedient servant. If they don’t act like a much better disguised and quicker version of zombies, they show a fanatic obsession to Slender Man akin to religious fanaticism. They often communicate through codes and cryptic messages, sometimes having their personality post-Slender Man shining through. It’s worth noticing that they are said to be unable to do even the simplest things necessary to stay alive when they are not on a mission for Him. Again: First explanation by Reach, while the term was probably first featured at all in The Tutorial.
Proxies/Slenderproxies – Another term for Black Pawns, but more often than not referring to everything but Agents/Servants. Source unknown to me.
Revenants – A kind of Proxy mostly known about in rumours. They are said to have risen in the hierarchy enough to obtain own powers akin to that of Slender Man, albeit not as strong as His. There are very few of them and since they are less expendable than other Proxies it is rather unlikely for a White Pawn to come in conflict with one of them. Instead they seem to be used for organisation purposes. Their sanity seems to range between the status of an Agent and a Berserker, since they are clearly able to use their Free Time however they want, but also bend to the will of Slender Man. Mentioned by Reach, too – who stated that he was one of them.
Servants – A more recent term for Agents. First mentioned on Walking the Hallowed Halls.
Sleepers – People who are under control by Slender Man, but are not aware of that. They lead an usual life for most of the time and can never remember what they did under Slender Mans influence.While in Proxy mode, they act the closest to Hollowed, but can range to the sanity degree of Berserkers at least. Some White Pawns may actually (or also) be Sleepers. Also explained by Reach.
Taken – A more recent and neutral term for Hollowed and maybe Berserkers. While Hollowed may also refer to people being able to make very weak efforts on surviving, Taken rather describes Hollowed really unable to do anything not necessary not carry out an order by Slender Man. While Hollowed is used mostly by White Pawns who only see their behavior in mission mode, insider Andrew from Walking the Hallowed Halls raised this term in describing them from the point of view of an Agent/Servant. This is why I’ll mention separately here that they are described as being thoroughly mad, only using their codenames for each other, obsessed with masks and stalking people. Andrew also mentioned something like possibly telepathic communication [Andy Note: think "hivemind"] between them, since they have been seen interacting with each other without exchanging words while clearly showing signs of conversation. Servants obviously are not able to take part in the mental communication between them, possibly due to “too much” sanity.
Touched – Another term introduced by Walking the Hallowed Halls. It can be used as another word for Proxy, but most often it’s definition ranges from Sleepers over Revenants to Berserkers. Some Agents/Servants too have chosen to be what they are because they are – albeit in a weaker form – Touched. Basically the term refers to having had close contact with Slender Man, used by Him to transfer sensations to the human being which are not fit for the human mind or oppressing their will with His own for a while. Being mentally touched by Him this way sooner or later is said to lead into insanity, although Slender Man seems to have a certain amount of control over how long it takes to transform a person from a Touched into a Taken.