Custom Pos/Neg Feat

[Dwoops]

So, I have a friend who is a DM and likes to give his players a kind of +1 feat -1 feat at first level. By this I mean they get something special to their character that is beneficial and detrimental with about the same power as a feat. This is meant to add some unique character creation ideas in order to make each character seem special. It also helps with forming the personality of the character if used properly. Also note that this DM primarily does Pathfinder, which I feel is more free with giving out feats. For those who don't know, in pathfinder feats help shape your class to fulfill whatever niche you want, so you get quite a few(I also am not an expert on pathfinder so I might have this wrong). Given this, I am attempting to implement it into my 5e game because I thought it would be a fun way to make my players more invested into their characters. It also helps with letting them customize how they want their character to be, a bit.

Now to the problem. I have a player who want to make a character that all about agility and stuff. To this end they won't wear armor, even if it helps them and in return they want a movement speed bonus to help them get around. While I have no problem with this sort of exchange there are a few balance points I'm not sure on.

First, the negative is absolutely pointless if they have natural armor or are a monk/barbarian. I already know they won't have natural armor as they want to be a Tabaxi, but they are trying to decide between monk and rogue. Given this, if they choose rogue I think I'd be fine with not letting them use armor (about -2 ac) and getting extra speed instead. I think -2 ac is a pretty big deal since this effectively caps their AC at 15 or so (17 with a shield, but they aren't planning on using one). To offset this, I was think 10 or 15 speed would make sense, or maybe speed = flat dexterity or speed = dex mod*5? I would like some opinions on what would be balanced.

For the monk however, due to their wisdom turning into AC when they don't have armor on, this kind of defeats the purpose of the negative balance. So if they end up choosing monk I would need some other negative effect to offset their movement increase. Does anyone have any ideas (and corresponding +movement speed that is balanced)? The only possible negative effects that I can think of are things like reduced movement speed in water or climbing, but I don't know.

Any help would be appreciated, thanks.

[stoutstien]

Sounds like the flaw system from 3.x.
Most players will gladly take a -1 in int for a +1 in an other stat so it can be iffy.

[Dwoops]

Sounds like the flaw system from 3.x.
Most players will gladly take a -1 in int for a +1 in an other stat so it can be iffy.

Part of why I am not letting them alter stats, of course people would min max with dump stats if they are looking for power. I am meaning this to be more of a character quirk that focuses gameplay a bit. Kind of like with the rogue version, in order to stay alive, kiting is more important than AC. It alters the way the character plays to fit whatever the person wants, balanced by the DM of course.

[Ventruenox]

A lot of the core class features already have that built in to the system. Monks get the increased speed, Rogues get Cunning Action, etc. Playing around with those mechanics too much leads to imbalance in the game. Offering Inspiration points for playing up a character flaw might probably be the best way to go. I personally prefer expanding on the FATE Aspects (https://fate-srd.com/fate-core/making-good-aspect) than simply pulling from the 5E background flaw list.

[DeTess]

I wouldn't make it about banning armor,as having a high AC can be part of the whole mobility thing (dodging attacks). Instead, I'd play up the 'fragile speedster (https://tvtropes.org/pmwiki/pmwiki.php/Main/FragileSpeedster)' trope and have the negative be something along the lines of 'disadvantage on con saves' or 'gain 1 less hp whenever you gain a level, including your first'.

[Dwoops]

I wouldn't make it about banning armor,as having a high AC can be part of the whole mobility thing (dodging attacks). Instead, I'd play up the 'fragile speedster' trope and have the negative be something along the lines of 'disadvantage on con saves' or 'gain 1 less hp whenever you gain a level, including your first'.

I like the less HP idea, kind of class cannon dodgy style. I feel like disadv on all con saves seems like a very large deficiency since con saves are common (at least how I DM). Monks and rogues both get a d8 per level, maybe rather than making it a -1 (because then if they have 0 con modifier and roll a 1, then they wouldn't gain any hp), Ill just say the HP(and hit dice) is now based on a 1d6. How much speed do you think that much hp is worth. This campaign is lvl3 till whenever it stops, so this could be quite the effect over time. If i remember correctly, the ave for a d6 is 3.5 and d8 is 4.5, so that is a net -1hp per level. I haven't actually DMed a game past lvl 8 yet (only 2 short campaigns of experience, about 6 months) so I'm not 100 certain with some balancing aspects. Movement speed is one of those things that I don't know how to balance properly, its combat effectiveness is kind of abstract and in many other circumstances it is limited by the speed of the party. Still, movement speed is really useful, so I view it as a relatively strong buff. Given this, either 10-20 ft or 5*dex mod ft additional seems fair. Does that sound about right for decreasing the hit dice by 1 dice level?