Con saves? I know I've missed some pages but did they swap over to 5th ed or something?

I've said reflex during 5e games. And dex in pathfinder games. Just happens sometimes when you play multiple systems.

They have been running for a minute, after that you have to make saves to keep going, based on constitution. I don't remember if you just take nonlethal damage if you keep going or if it stops you from being able to move as fast for a time, but penalties start happening

Base stat saves occur in 3.5 and Pathfinder too; but they are for things that are supposed to be a lower chance to pass unless you are built for it. Running for too long would be CON saves over fortitude according to the rules, since, at least in Pathfinder, CON is bound to a specific range so it's possible to keep the same Save Value at all levels. Same is not true of Fortitude, which gets increasing bonuses that can result in either needing different saves for different levels, or having classes that are just built to run forever.

Oh yeah, I have a vague memory of the feat Endurance giving a bonus to those.

Seems like someone keeps casting "Summon Bigger Fish"

Might to be hinting at the departure from this map?

*Might you be