Jagex has already made some small improvements to the boss's common loot, and has expressed interest in making more changes in the coming weeks as more data becomes available. The following are some items I feel should be added to more accurately fit it's lore, and to make it overall more worth doing without reaching Callisto/Nightmare levels of gp per hour.
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A dragon item- The Hueycoatl is a draconic creature. Dragons were created by the Dragonkin, which is the only race capable of forging orikalkum. Most dragons in the game already have some type of dragon item on it's loot table. For example, Wyrms drop the dragon harpoon, dragon knives, and dragon thrown axes. I suggest giving the Hueycoatl at least one dragon item to drop for this reason. How about replacing it's adamant bolts (u) drop with dragon bolts (u)? Or replacing the rune dart tips with dragon dart tips?
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Noted Runite/Adamantite/Gold ore- The Hueycoatl is capable of burrowing through mountains. The dwarves of Cam Torum are even fearful of the beast tunneling into their underground city and causing mass destruction. According to legend, it is also said to "sleep upon a pile of gold". Therefore, it would make sense that such a creature would possess valuable ores that it found underground.
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Replace earth runes with mud runes- I don't consider earth runes to be a suitable drop for a level 642 monster. Mud runes have more value due to making it easy to cast Boost Potion Share, Stat Restore Pot Share, Bones to Peaches, etc. And it makes sense thematically because the creature comes from underground. These runes are already dropped by a number of monsters anyway, such as Daggonoth Prime and Chaos Fanatic. It shouldn't hurt to include them as loot at Hueycoatl.