While the PCs are traveling a road, they suddenly hear the beating of hooves coming from behind them. The next thing they know, a laden packmule gallops by, speeding into the distance - and right behind it is a stout man in fine clothes, his legs pumping at the air and his chest heaving as he pushes himself to run as fast as he can.
The man is Irakles Konstantinidos, an itinerant merchant who was traveling the road with his mule, Primrose, when she suddenly spooked and broke free of his control, taking off down the road. The mule is carrying a valuable load of merchandise, as well as the wealth Irakles has obtained from the last market he visited - a fact that is quite evident from the sounds of jangling coins coming from the beast's saddlebags. He implores the PCs to help him catch the mule, and retrieve the loot.
If the PCs decide to join the chase, enter Action Time. The party begins 90 feet away from Primrose, and she always makes the first turn of each round. She is in a panic, and will try to move as far away as she can from the party, taking a Dash action on each turn (moving 80 feet away) unless otherwise impeded. Irakles joins the initiative order as normal; he has the stats of a commoner. He emphasizes to the party that the mule is carrying valuable cargo, and he needs her for his profession. The PCs must catch up to the mule and slow her down without harming her or the treasure she carries.
The PCs may try to catch up to Primrose with their movements, or use items, magic, or other effects to try and slow her down. A PC may attempt an Animal Handling check opposed by a Wisdom save from the mule to try and calm her down. If this check succeeds, she does not move on her next turn, allowing the PCs to close the gap some. As usual, you should allow the PCs to come up with logical solutions to the problem and use your judgment in determining whether or not they would work, and the ramifications thereof.
At the beginning of each round, roll 1d20 for a complication that must be dealt with (by both Primrose and the party) that turn:
1. Poor visibility (such as dust clouds or wind). All creatures must make a DC 10 Perception check or have their speed halved for the round.
2. Obstacles block the path (such as logs, trees, or large rocks). All creatures must make a DC 13 Acrobatics or Athletics check to bypass the obstacle or have their speed halved for the round.
3. The ground becomes rocky and uneven, acting as difficult terrain. Creatures must move at half speed for the round unless they have some way of circumventing the terrain.
4. One creature determined at random must make a DC 13 Acrobatics check or trip and fall prone for the round.
5. The path is straight ahead, and could easily be traversed in a sprint. Each creature may move two times their normal movement speed this round (four times if using a dash action!), but must make a DC 12 Constitution save if doing so or take one level of exhaustion.
6. One creature determined at random must make a DC 13 Acrobatics check or get their foot stuck in a hole. They gain the Restrained condition until they can make a DC 13 Acrobatics or Athletics check on a future turn.
7. The path takes a steep slope upward. All creatures must make a DC 13 Athletics check or have Disadvantage on all actions for this turn. Alternatively, they may take one level of exhaustion to bypass this effect.
8. A barrier blocks the path forward (such as a fallen tree, stone wall, or fence). All creatures must make a DC 12 Acrobatics or Athletics check to jump over the barrier or lose a turn as they waste time climbing over it.
9. A hazard of some sort (like falling rocks or brambles) is in the path. All creatures must make a saving throw appropriate to the actions they are taking to avoid it; on a 1-9, they take Dangerous damage; on a 10-14, they take Setback damage, and on a 15-20, they take no damage.
10-19. No complications arise this round.
20. The PCs are unusually lucky. Each PC may take an extra action this turn.
If the party manages to catch up to Primrose, they are able to grab hold of her and she grinds to a halt (optionally, the DM may require a PC make a successful Grapple check in order to do this). If more than 200 feet elapse between Primrose and any party member (including Irakles), she is lost and nowhere to be found. Optionally, there may be tracks left, which may lead the party on another adventure to find the beast.
Note that Irakles insists it is very important that Primrose be returned alive, and with the load intact. As he puts it, he would not be a very good merchant if he had neither wares to sell, nor a means to carry them. If the mule is harmed, or the merchandise lost, he will not be happy.
A less scrupulous party may realize they could obtain a mule and some treasure for themselves if they could find some way of dealing with Irakles! Primrose's saddlebags carry in total 4,110 GP's worth in coinage (1,000 copper coins, 8,000 silver, 2,100 gold, and 120 platinum), plus 14 rolls of textiles worth 50 GP each. The textiles will need to be taken to a market to trade with, and they are cumbersome to carry; each weighs 5 pounds.
If the PCs do recover the mule unharmed, Irakles will be thankful for their efforts. They may run into him again in another market; if so, he will sell them his goods at half price as a show of gratitude. He also may have knowledge of surrounding areas to share.