2 years ago (edited)
When you're sneaking up on someone and you cast a bonus action spell (like Hunter's Mark) triggering combat, you start your turn without your action, while you should have only consumed the bonus action to cast the spell. Not game-breaking or anything, it's a very fringe case. But for a ranged Ranger not being able to use Hunter's Mark in your surprise round is mildly annoying. You can go around this by starting combat with a Fire Bolt from your Wizard, but still.