So FYI, these Chase rules are somewhat inspired by my 10 or so years of playing rugby. I understand why people may want to use regular Athletics (Strength) or Acrobatics (Dexterity). It probably wouldn't break anything doing so. But when you are running as fast as you can while chasing, tackling, dodging, passing, keeping your head on a swivel to keep your situational awareness... it doesn't matter how strong, quick, or agile you are. If you don't have gas in the tank, you can't maintain that kind of action for more than a few seconds. And from my perspective, a good rugby phase is a near perfect real-world equivalent for a chase. I know a lot of people have been comparing the chase to an Olympic sprint, which is fine. But often in a chase you are running through a crowd, jumping a fence, ducking through alleyways, avoiding trees, dealing with the sudden influx of cabbages rolling about after the someone accidentally burst through the cabbage vendor's cart as he shouts "NOT MY CABBAGES!"... you get the point. So if you find my system to be a bit Con heavy, that's why.
The spell rules feel a bit overly complicated to me. Instead of making spells crappy, I would just increase the risk of using them. Have it give a big penalty to the chase roll (and no level scaling just a single penalty), but the spell works as normal. Or if you just say that casting a spell delays you a square...so it’s a big slowdown.
So the reason for the spell changes is to reduce how much of an impact they can have on a chase. It's like the classic trope you see in movies where when a person is being chased by an enemy lobbing ranged attacks at them. The person is never directly hit by any of it, but things are blowing up all around them and may trip them up. Because everything is on the move, accuracy goes way down and offense is just generally less effective. So that's what I'm going for. It may not be perfect, but for me it kills two birds with one stone (reducing the insta-stop capacity of spells, and emulating the trope mentioned above).
I get the penalty to armor...but that is not the 5e way. 5e is very comfortable with armor, you can sleep in it, it has no endurance penalties, etc. it really should not be a factor in the rules, other than if it slows you down which you already account for.
That's not completely true. It's expanded a bit in XGtE, but it is true that generally you get no penalties involving light armor. But for example, if you sleep in medium or heavy armor, you only regain half your normal hit dice and do not reduce any levels of exhaustion you may have. Additionally, several types of medium armor and all heavy armor causes disadvantage on Stealth checks and, if you don't meet the strength requirement, heavy armor reduces your speed by 10ft. Not to mention a chase is not a normal situation. Armor may not impact general activities, but from my perspective, it absolutely impacts any situation in which you are exerting maximum effort over a prolonged period of time (more than a round). If you had two people of roughly equivalent athletic capacity running an obstacle course, but one was in armor, I would always bet on the non-armored person to win. So while they may not be used often, 5e does have rules that make it harder to function in Medium or Heavy armor. And even if those penalties are not as explicit in the 5e design philosophy, I think they fit well with what I'm trying to achieve with these Chase rules.
you may want to note in your exhaustion section when exhaustion slows down your speed to half, as that is a big deal for your chase checks. It’s just a quick reminder for players.
That's a good point. Perhaps just putting up all the exhaustion levels would be good, since even 1 level of exhaustion means you will be rolling your Chase roll with disadvantage.