DMing Help: A Curse Disguised

Loooooong story short: One of my players is a warforged artificer who was originally a wizard working at an institute of strange, magical, and dangerous items. He became a warforged after he accidently found an ancient artfact that was hidden away and experimented on it. While he was experimenting on it, it killed him and the machine that was designed to enclose it to prevent it killing everything closed and killed the character and then he had his soul transferred into the machine. Full Metal Alchemist type of situation according to the player when we were working it out.

You see, this worked REALLY well because the point of the campaign is the find 5 artifacts from 5 islands. What the players don't know is A. the warforged's core IS one of the artifacts (even the warforged isn't aware of this) and B. All 5 items are seals to keep away an ancient evil. This ancient evil has begun speaking to the warforged, talking about how it saved them from fully dying, their ideas and trying to understand what is going on and lead the warforged into setting it free.

Now, I don't wanna make this too obvious. But I also want him to have a benefit from helping this creature to incentivize him to keep doing it. My problem is figuring out exactly how. Do I make it a magical item that upgrades the more he "consumes" (absorbing the life of the land and creatures he kills)? Do I make it a feat? How do I make it sound useful and not evil?

TLDR: Trying to make a Curse sound like a Blessing to trick a player into helping the BBEG but unsure how to approach it. Help

Uhhh.... 

I see a couple potential problems. 

A) the player is going to potentially get a lot of the spotlight

B) the player will be railroaded into this circumstance

C) the player will be railroaded to get out of this circumstance.

Yeah, I would be very concerned with player agency here. What if the player doesn't want the magic item or feat? Also, it's usually better to have a group version of "you've secretly been helping the bad guy and didn't know it" rather than pinning that on one player.

All of them will eventually get one of the 5 items. He just has one by pure chance. There's 5 players and I have each mapped out on who is likely to get the other 4.

Use a corruption mechanic, sure use it to short cut encounters, but gain points, as you gain points get better at directing the power, but realise you are losing control, and you only ever gain points, so by all means hog the spot light and do incredible things but you will either not use it for the latter half at all or you will fall to the artefacts malign influence.

I'd start by asking what the Warforged player will have to do to set this thing free. Like, will this be a choice they have to make? "Free me and I'll help you!" type of thing? Or can it just be that the artifact needs a certain amount of power so that the being inside can grow strong enough to break free? I'd also ask what the relationship will be between this and the other four artifacts. What will the other four players have going on with their artifacts? How will that relate to the BBEG?

I really like the idea of the curse in disguise, that can be very cool! Just as someone else mentioned, I'd be careful not to make the Warforged the star of the show.

I think my biggest suggestion might be to tweak the consequences to make this about the player. Instead of making it about whether or not the Warforged sets the BBEG free, I might have the consequences of the curse fall on the Warforged player themselves. My immediate thinking is to have the evil spirit make the player an offer. If they accept, they get some version of a Dark Gift (from the Ravenloft book).

Although I might brainstorm... I think the options in the Ravenloft book are a good start, but they're kind of limited and pretty weak on the downsides.  But I think the core concept could be really good for what you're looking for! The player gets a fun arc, but the entire campaign doesn't rely on them making a certain decision.

Quote from MelMightyena >>

All of them will eventually get one of the 5 items. He just has one by pure chance. There's 5 players and I have each mapped out on who is likely to get the other 4.

Yeah, so, i see some possible issues here, namely that all the players have to get a cursed item to complete the campaign?

Im in a campaign where we have found half a dozen cursed items and theyre all in someones bag of holding cause no one wants the curse.

Someone picked up an item and got cursed, they didnt want it, so we cast remove curse and it was over.  I picked up an item and it was supposed to make me roleplay a certain way and i didnt want that.

I cant imagine any player willfully picking up some item that causes a supreme evil being to talk to them and try to get them to do things they dont want to do, unless you withold normal, uncursed magic items and basically force/bribe them to take thr cursed items.

The mcguffins are not the important part of the campaign. The players are. If you force the players to carry the items so it messes with them rather than just let them collect the mcguffins and put in a bag of holding so they can play how they want to actually play, youre going to end up with some very frustrated players.

Well, instead of having the player kill things and absorb them or whatever, you could have the evil give them a task to do to "pay off their debt". Tone it as helping them keep "that horrible evil" sealed. The whole party will hopefully get involved to help this player carry out their tasks.

The short story is: players generally won't willingly help a great evil. Either the great evil needs to be completely disguised and no bad thing can come from helping it until the very last moment, or they must have no choice in the matter. 

So you could have the artifacts just be powerful magic items that are all connected to each other, but it is completely unclear their origins or what their large scale purpose is. They should be straight up boons with no curse or negative side effects, nor anything creepy or evil seeming about them. 

Alternatively, you could have the great evil be able to turn off the artifacts at will, thus is capable of killing the warforged at any moment. The great evil uses this ability to coerce the party into helping it while the party tries to find a way to break the warforge's reliance on the great evil without the great evil figuring out what they are doing.

"you could have the great evil be able to turn off the artifacts at will, thus is capable of killing the warforged at any moment. The great evil uses this ability to coerce the party into helping it while the party"

Yeah, thats the subplot with Thanos getting the Infinity Stone out of Visions forehead. The only winnable option would be for Vision to off himself so that the party can get the stone and keep it from thanos.

The alternative is what happens in the movie. They try and fail to remove it safely, then vision begs someone to remove it from him even if it kills him, and then thanos shows up, kills vision anyway, gets the stone anyway, and was literally one of the dumbest subplots of a movie ever.

Personally, if i were the player running the warforge, id kill myself so the party can remove the artifact without delay and without guilt, keeping it from the bbeg, and then id just roll a new character. On top of all the other benefits, id have a character free of any railroading effects.