1. Attacking with a Light weapon lets me make a bonus action attack with another Light weapon
2. The Nick property allows me to make this extra attack as part of the attack action, but if I don't need to actually use a weapon with the Nick property to get the benefits of nick then I would be able to use any Light weapon for this.
Yes this is true. You can use any Light weapon for the attack that the Light property gives you. It doesn't need to have Nick on it.
Like, I can wield a shortsword in one hand and a hand crossbow in the other and when I use the Attack action to attack with my shortsword, I can then fire my hand crossbow using the Light property (Bonus Action needed here). No Nick property necessary.
With the nick property, I can wield a scimitar in one hand and a hand crossbow in the other and use Nick to attack with both as part of my Attack action. I don't need the second weapon to also have the Nick property.
Where the Pact of the Chain comes in is that it lets you swap out
any attack made as part of the Attack action. (EK's War Magic has the same wording, for another point of comparison).
Based on RAW, the limits on that attack don't look like they matter, aside from the action you use to make it.
If you can only make a ranged attack?
If you can only make an attack with a Light weapon?
If you can only make an unarmed strike?
If you can't actually deal damage with the attack?
If you can only make the attack against yourself?
If the Cleave property granted you the attack?
If it's an attack granted to me by an ally?
All are "attacks" and so seem to be valid to swap out -- there's no requirement that the swap that Pact of the Chain or War Magic lets you do has to be a certain kind of attack or an attack with certain properties, aside from the action requirement.
Nick only applies "when you make the extra attack of the light property" no extra attack of the light property == no nick.
Hmm...this seems to be a bit of a grey area in terms of Order of Operations. When can I make the swap that Pact of Chain / War Magic lets me make?
- I use the Attack action. This satisfies the conditions of the swap: during this action, I can swap an attack.
- I make an attack with my Scimitar. This satisfies the conditions for the Light property -- I can make an attack with a bonus action with another Light weapon.
- Because of the Nick mastery, when I make this attack, it can be part of the Attack action.
- Now that I have another attack that can be used as part of the Attack action, I make the swap.
The Attack action and the extra attack of the Light property are happening as part of the Attack action, and if it's an attack I can make as part of the Attack Action, it's swappable
vs.
- I use the Attack action, satisfying the conditions of the swap.
- I attack with my Scimitar, satisfying the conditions for the Light property
- Because of the Nick mastery, when I make this attack, it can be part of the Attack action.
- I cannot make the swap, because the Light property requires me to use a specific kind of attack only.
And point 4 is where things get iffy for me, since I can still apply any other modifications to that attack that are valid that I wish. I can choose targets, use bardic inspiration, add a damage rider, etc. Like, if I have the Two Weapon Fighting feat, it clearly lets me modify the attack granted by the Light property. There's no reason I can see why I
can't modify the attack by swapping it out. The general requirements of the Light property don't matter at all to the swap's specific language.
The swap is pretty expansive in its reference to attacks made as part of the Attack action. It doesn't seem to care much about the source or limitations on those attacks.