How would you fit Crossbows into this?
For the most part, Crossbows wouldn't fit into this. Crossbows already have their own feat (Crossbow Expert), and a feat that can be used with crossbows (Sharpshooter).
Learning to use a Mighty Bow (a powerful composite shortbow, an English longbow, etc.) is very different...and harder...than learning to use a crossbow. Some aspects learned from using Mighty Bows do cross over when using Crossbows, and some aspects learned from using Crossbows do cross over when using Mighty Bows; but overall, training in Crossbows does not provide training in how to use Mighty Bows...and it shouldn't.
Historically...in real life...Mighty Bows like the English Longbow, took almost a decade of practice with them to gain real proficiency; to gain a level of proficiency suitable for the battle field. Crossbows could be learned by anybody, and very quickly. This aspect is the primary reason why crossbows are
simple weapons, and why they were decried as evil weapons, with many governments and the church oft attempting to ban them.
However, parts of the feats, like the one's they are adapted from (specifically Crossbow Expert), are not written with language specific to Mighty Bows, and therefore should be allowed to be applied to crossbows also. I think the Crossbow Expert Feat was purposely written that way, or if it wasn't, is at least my interpretation. The parts that are non-specific are:
• Being within 5 feet of a hostile creature doesn’t impose disadvantage on your ranged attack rolls.
• Before you make a ranged attack, you can choose to take a - 5 penalty to the attack roll. If the attack hits, you add +10 to the attack’s damage.
...which are exactly the same as from the Crossbow Expert feat. If you have learned these aspects with Mighty Bows, I see no reason why you wouldn't be able to use them also with Crossbows, and vice-versa. The only parts you don't learn this way are:
• You ignore the loading quality of crossbows with which you are proficient.
For this aspect, you need to actually take the Crossbow Expert Feat...as it should be. Nothing about learning to use a Mighty Bow gives you expert proficiency and increased speed with loading a Crossbow.
And...
• You gain an extra attack when using the attack action on your turn, for a ranged attack with a shortbow or longbow that you have proficiency with, in addition to any extra attacks provided by your class.
For this aspect, you need to actually take the Mighty Archer Feat; and it should never...ever...EVER apply to Crossbows. Turning Crossbows into medieval machineguns completely negates the uniqueness of English Longbows and Composite Shortbows. Which is why the Master Archer Feat specifically states it's for use only with shortbows and longbows, and why the Mighty property is specifically limited to shortbows and longbows.
I agree, but I think the Feat "MIGHTY ARCHER EXPERT" is OP, reduce it some, it looks like you have added multiple Feats into one
Mighty Shortbow, Longbow or Crossbow; 25% increase in price for each point of Strength
Weapon Master Feat
• You can utilize bows that have the "Mighty" property; STR score of up to 20.
• You can utilize crossbows that have the "Mighty" property; STR score of up to 20.
• You can utilize Ballista with proficiency.
• You can utilize cannons with proficiency.
(you don't need to make a new feat)
Sharpshooter Feat
Crossbow Expert
• Being within 5 feet of a hostile creature doesn’t impose disadvantage on your ranged attack rolls.
• Before you make a ranged attack, you can choose to take a - 5 penalty to the attack roll. If the attack hits, you add +10 to the attack’s damage.
There are a few points here I'll address, though possibly not in the order of presentation.
First, there's no such thing as a Mighty Crossbow; or more accurately, Crossbows as constructed are already Mighty Bows...though this would by no means provide proficiency with Mighty Bows.
Crossbows (with maybe the exception of hand-crossbows) cannot be drawn and cocked simply by hand; they require at least the use of a foot and both hands to draw, or mechanical assistance. The bows of crossbows are made from materials that could not be drawn, no matter how much training, in the manner of a shortbow or longbow. They are already made from far heavier and stiffer wood than even an English Longbow or an Eastern Composite Shortbow, or not even made from wood at all (steel...mithril, adamantium, etc.).
Second, training to use cannons and ballista also have nothing to do with the specialized training for using Mighty Bows. The skills simply, for the most part, do not cross.
Third, I went with a price increase for every two points of strength simply because making a bow with an odd-numbered strength would be a waste of money (it doesn't provide a bonus increase). Effectively, the only numbers that matter for these bows will be the even numbered STR scores.
Also, I wanted to make it a flat amount so it's easier to figure out the price - simple addition. Having people figure out percentages, especially when no other rules or mechanics in the game use percentages, seems like adding complexity when it's not necessary and introduces inconsistency to the structure of the rules.
Fourth, I don't see anything in the Mighty Archer Feats that steps on or duplicates the Sharp Shooter Feat. And the Sharp Shooter Feat can still apply unchanged.
Fifth, I think the Weapon Master Feat is a poor fit for what we are trying to do. Primarily, learning to use a Mighty Bow (English Longbow, Eastern Composite Shortbow, etc.) is a very specialized training; training that doesn't include training in other weapons. It makes no sense why learning how to use a Mighty Bow, would also mean you suddenly know how to use three other totally unrelated weapons.
Personally, I think the Weapon Master Feat is poorly envisioned and written. I understand its purpose, to allow characters to learn weapons not provided by their class, but it does have issues. One, it gives proficiency with four weapons mostly because to not do so, would leave the Feat vastly under-powered relative to what other Feats provide. That's a purely mechanical comparison and mechanical solution, devoid of connection to any real concept or higher truth; and I personally despise such machinations. And two, it can provide proficiency with completely unrelated weapons all at once...something that just doesn't make sense. "
Master" evokes "Expertise"..."Specialization"..."Exceptional"...and not merely Proficient. I imagine it wasn't titled "Weapon Proficiency", despite the fact that this is all it is, because that doesn't sound "Cool"...doesn't fit with the titles of the other Feats. However, fixing that Feat goes beyond the scope of this thread, and beyond the scope of what I want to delve into at this time (as it would likely mean for me, digging in and revising almost all of the Feats). So, I'm just going to ignore Weapons Master for now.
Lastly, I see what you're saying about the Expert feat, though I don't think it's over-powered. I do however feel that it has too much "stuff" in it.
I'm going to shift the increased attacks aspect to the first feat: Mighty Archer. I think that would better model the extra attacks that such weapons provided in earlier editions, give the Mighty Archer feat a little bit more than just simple proficiency, and even model the role of such weapons in real life - that of the heavy machine-gun of the medieval battlefield. The increased rate of fire was the main advantage over crossbows, while the advantage of crossbows was similar force/damage and range, but was easy for anyone to learn and use.
So, revised...and for me...final versions.
MIGHTY ARCHER
Thanks to extensive specialized practice with powerful bows (Mighty property), you gain the following benefits:
• You have proficiency with bows that have the Mighty property with a STR score of up to 18.
• You gain an extra attack when using the attack action on your turn, for a ranged attack with a shortbow or longbow that you have proficiency with, in addition to any extra attacks provided by your class.
MIGHTY ARCHER EXPERT
Thanks to further specialized training with powerful bows (Mighty property), you gain the following benefits:
• You can utilize bows that you have proficiency with, that have the Mighty property with a STR score of up to 20.
• Being within 5 feet of a hostile creature doesn’t impose disadvantage on your ranged attack rolls.
• Before you make a ranged attack, you can choose to take a - 5 penalty to the attack roll. If the attack hits, you add +10 to the attack’s damage.
WEAPON PROPERTIES
New Property
Mighty. A shortbow or longbow with this property has it's own STR score. A character must either possess proficiency in bows with this property, or have an equal or higher STR score, to utilize them. You may add the STR bonus of your bow (if higher), instead of your own DEX bonus, to attack and damage rolls when attacking with a mighty bow. You may not add your own STR bonus (if higher than the bow) to attack and damage rolls. The range of any shortbow or longbow with this property is increased to 200/800. Damage dice are increased from 1d6 to 2d4, or 1d8 to 2d6. The price of shortbows or longbows with the Mighty property increase by 25gp for bows with a STR score of 12, with an additional 10gp for every two points of STR above that (+25gp for STR 12, +35gp for STR 14, +45gp for STR 16, +55gp for STR 18, +65gp for STR 20, etc.).
Cheers.