one of my players wants to make armor out of siren feathers. The question isn't how, but more so what. Would it still have the base 18ac? would it be light armor? in that case do you add dex mod? all those questions.
The easiest thing is to probably pick the stats of one of the existing armors and add some bonus on top of that - either +1 AC, or something appropriate to siren feathers.
The Siren doesn't have feathers and is a chaotic good creature, I'm not sure that would be a great choice to make armor from. I could actually see it as a component to possibly add a magical effect to an armor or item, like granting magic resistance which the Siren possesses.
First, you'd need to specify the Siren we're talking about. If you're talking about the official creature from Tomb of Horrors, it's AC is 10+dex mod - so the feathers are giving 0 protection.
You could do something like wtf recommends and have it grant an ability - magic resistance makes the most sense here, but you need to be careful here. That's a pretty powerful bonus and it was practically free. Your party will start wanting to harvest all kinds of creature parts and expect significant bonuses from them.
If you really want to do a Monster Hunter style thing where you're crafting stuff from monster parts, you need to overhaul your magic item distribution and figure out a crafting system. It's a lot of work to keep things fair and avoid overflowing the party with magic items. I've done this in my campaign - crafting components are dropped from monsters or harvested in the wild and can be used to upgrade equipment. But this replaces most of the treasure they would normally get and I'm constantly having to make new recipes and figure out what kinds of powers a particular monster might be able to grant. It's a lot of work.
If I were you, I'd just tell them they can adorn their armor with the feathers but it wouldn't have any significant game effects. Maybe it would be worth a small bonus to performance or intimidation checks in certain situations depending on who you're interacting with.
one of my players wants to make armor out of siren feathers. The question isn't how, but more so what. Would it still have the base 18ac? would it be light armor? in that case do you add dex mod? all those questions.
Totally up to you as DM.
The easiest thing is to probably pick the stats of one of the existing armors and add some bonus on top of that - either +1 AC, or something appropriate to siren feathers.
The Siren doesn't have feathers and is a chaotic good creature, I'm not sure that would be a great choice to make armor from. I could actually see it as a component to possibly add a magical effect to an armor or item, like granting magic resistance which the Siren possesses.
First, you'd need to specify the Siren we're talking about. If you're talking about the official creature from Tomb of Horrors, it's AC is 10+dex mod - so the feathers are giving 0 protection.
You could do something like wtf recommends and have it grant an ability - magic resistance makes the most sense here, but you need to be careful here. That's a pretty powerful bonus and it was practically free. Your party will start wanting to harvest all kinds of creature parts and expect significant bonuses from them.
If you really want to do a Monster Hunter style thing where you're crafting stuff from monster parts, you need to overhaul your magic item distribution and figure out a crafting system. It's a lot of work to keep things fair and avoid overflowing the party with magic items. I've done this in my campaign - crafting components are dropped from monsters or harvested in the wild and can be used to upgrade equipment. But this replaces most of the treasure they would normally get and I'm constantly having to make new recipes and figure out what kinds of powers a particular monster might be able to grant. It's a lot of work.
If I were you, I'd just tell them they can adorn their armor with the feathers but it wouldn't have any significant game effects. Maybe it would be worth a small bonus to performance or intimidation checks in certain situations depending on who you're interacting with.
My homebrew subclasses (full list here)
(Artificer) Swordmage | Glasswright | (Barbarian) Path of the Savage Embrace
(Bard) College of Dance | (Fighter) Warlord | Cannoneer
(Monk) Way of the Elements | (Ranger) Blade Dancer
(Rogue) DaggerMaster | Inquisitor | (Sorcerer) Riftwalker | Spellfist
(Warlock) The Swarm