Tumble melon trees are large, wineglass-shaped trees with thick limbs and greenish bark. They reproduce in an unusual way: they produce delicious roaming melons with mild curative properties. After the melon seeds pass through the body, they compel the creature to plant them somewhere fertile.
Groups of these wandering fruit depart simultaneously every few weeks (in different directions). The tree rolls the melons down grooves in its trunk, and thus sets the traveling melons on their trajectories. If a tree is approached, there is a 50% chance that it will flat-out give you a melon. If the tree is climbed, it will wiggle in an attempt to shake the climber off. If the tree is attacked or any melons stolen, the tree will freak out and start whomping people with thick branches.
If the tree is tormented with ranged weapons and there is no one nearby to whomp on, it may attack by throwing melons with its scoop-like 'hands'. It is difficult (but not impossible) to catch these melons undamaged. The traditional method of melon harvesting involves an archer and two assistants holding a 'catching blanket'. But even this is risky--tumble trees can throw a heavy melon very fast with their strong, whipping arms. A tree will usually have about 6-12 melons.
If a tumble melon tree is severely injured, it may feign death by making a sad wailing noise, going limp, and rolling any remaining melons in all directions. The melons will attempt, poorly, to avoid capture (they are in escape mode).
Tumble melons are about the size of cantalopes. The hard, leathery skin is colored in green and black zigzags. The fruit of the melon is pink, fleshy, and composed of pulpy seeds (think of a pomegranate). They roam by rolling in a random direction, although they avoid steep slopes and cannot manage anything more than the mildest uphill. They are common near rivers.
Tumble melons are roaming fruit. They have very poor senses, but they will approach creatures that they find and roll around their feet, like a cat asking to be petted. They are delicious, nutritious, and heal a tiny amount of health when eaten.
Sometime within 24 hours after being eaten, another magical ability of the melon manifests itself: it is a powerful laxative. Tumble trees reproduce by encouraging other creatures to spread their seeds throughout the land. The bowel movement will be watery, urgent, and include a great number of tumble tree seeds.
When the creature is pooping, the seeds also cast a charm effect on the creature, compelling them to bury the seeds in a safe place where a tumble melon tree might grow strong and healthy. If the seeds are ejected into loamy forest soil, all this charm effect does is require you to scrape some dirt on the seeds. If you are not in a sunny forest or a fertile field, the seeds will ask if they could please be buried in some nice dirt? You may be obligated to comply.
It is not recommended to exploit tumble melons for their healing properties. The laxative and charm effects stack dangerously with multiple ingestions. (You might blow your O-ring and spend the rest of your life pulling weeds in a grove of tumble melon trees.) Despite these prohibitions, it is not hard to find buyers for tumble melons, especially among opium addicts and others who suffer from constipation.
A Free Lunch. The PCs are accosted by a random wandering monster! Oh, it's just a delicious tumble melon, asking to be eaten.
At Least I Have Full HP. The wandering PCs randomly accost a tree! They stumble across a tumble melon tree. They've got a druid who knows half of the story, or an injured PC eats the melon and feels the healing powers of the seeds. Will they succumb to greed and temptation? And if they do, will they succumb to constant diarrhea and dehydration?
Come at Me, Bro! The PCs are tasked with harvesting melons from an adult tree. (For hard mode, make it a grove of them).
The Giving Tree. The PCs are badly injured, and come across a grove with a strange, naked man tending to the trees. He takes pity on the party and offers them fresh water and access to magical healing melons. A melon follows him around and seems to obey his commands, and the trees seem to give him melons when he asks. He tells the party not to eat more than one, and then slips back into unhelpful madness, talking to a sapling and becoming irritated if he bothered. The party is left alone in the tumble melon grove. After each eating a melon, they have felt the healing effects. Will they succumb to temptation and gorge themselves on melons until their bones knit and they are at full health? (Gods, I hope not.)