I was running what was supposed to be a one-shot recently, where the party was tracking some unicorns. The party's ranger used Hunter's Mark on one of the unicorns, who then used pass without trace. The party then decided to check on some nearby NPCs, except that they also wanted to call it a night, which is probably convenient for me.
The Pass without Trace spell description says:
A veil of shadows and silence radiates from you, masking you and your companions from detection. For the duration, each creature you choose within 30 feet of you (including you) has a +10 bonus to Dexterity (Stealth) checks and can’t be tracked except by magical means. A creature that receives this bonus leaves behind no tracks or other traces of its passage.
The Hunter's Mark spell description says:
You choose a creature you can see within range and mystically mark it as your quarry. Until the spell ends, you deal an extra 1d6 damage to the target whenever you hit it with a weapon attack, and you have advantage on any Wisdom (Perception) or Wisdom (Survival) check you make to find it. If the target drops to 0 hit points before this spell ends, you can use a bonus action on a subsequent turn of yours to mark a new creature.
The unicorns are probably going to be far enough away that the detection effects aren't really going to be involved. But the tracking part... Well, Hunter's Mark is definitely magical, but does a Survival check with Hunter's Mark count as magical? And how would that even work if Pass without Trace leaves no traces behind?