The Mechagoblin requires you to run several other runs first to obtain key parts, these key parts are then combined into the final key. In no set order the key parts required are:
Once you have one of each key, take them out of a container one at a time, they will react, and form into larger key parts, put these parts back into a container and take them out again, they will then form into A complex key, you may have to play around with the order you take them out with. Should you have multiple keys I would highly recommend taking them out using the full description quote method take "a curious-looking bit of a massive, complex key" trunk for example, then place them in a different container so you can play around with the order of taking them out.
Once your key is created, check your spell mems, and reagent levels, then head to Lowangen, from entrance go 2 north, 5 west, and down.
a chunk of a massive, complex key
a significant part of a massive, complex key
a hunk of a massive, complex key
the side bit of a massive, complex key (The New Kolvir blademaster key) goes clack as it attaches itself to the underside of a massive, complex key (Vextrinas, Priestess of Fire key).
a massive, complex key
The above 3 parts. Note that this key has a lifetime of roughly ~700 alyrian minutes.
Item 'a massive, complex key' is type key, alignment 0, made of iron, has keywords 'massive complex key'. This item weighs 0 stones and 26 pebbles, and is valued at 250 gp. This level 10 item has the attributes: identified A massive, complex key is in excellent condition. This key may be used 1 more time. *This item may be repaired 5 times. As long as your arm, this key finally makes sense. Comprised of seemingly unrelated bits of metal, but for their 'KEY' markings, the individual parts come together to form this regular-shaped key. Its size, however, is prohibitive. Whoever is responsible for it must either be huge or not go out very often. There is not indication where it leads to, but it's not as though it was terribly easy to make in the first place.
The Mechagoblin encounter
Once ready unlock the south, go south and The Mechagoblin will have fled up, follow up. Very straight forward fight, two people can easily kill it. Recommend the form setting defense to shield block as The Mechagoblin will fire rapid magic dart spam at people which can add up to a fair amount of damage. Note, the tank (assuming valkyrie, possibly anyone) should leave combat defense auto. It will not attempt to flee, and you will only be able to land a few spell ups on it (cannot slow). Make sure auto loot is kept on, and that any NPC's in form you may be using are ordered to flee or unformed as the corpse explodes pretty quick and you will lose any loot.
After the kill you can go right back down and wait for repop. Note that the room you wait in is no-regen, so take turns cycling form members regenning north of the noregen room. Once the Tinkergnome? comes back into his usual location north, have someone go north and close door, open door, and come back south, which will reinitiate the Mechagoblin. This can be done two additional times for a total of 3 kills on Mechagoblin. (Possibly can be done more depending on repop timings, but it locked and stopped working for us after we had killed 3 total times.)
Note: Killing blow will also be awarded 5-7 practices.
The Mechagoblin carries:
Item 'a lump of metal' is type treasure, alignment 0, made of unknown-alloy, has keywords 'lump refined metal relic keyrelic'. This item weighs 0 stones and 15 pebbles, and is valued at 4,750 gp. This level 75 item has the attributes: identified no-tweak A lump of metal is in excellent condition. *This item may be repaired 5 times. This lump certainly looks promising. It has no detritus in it, and it looks pure. It weighs a good amount, and has significant presence with its gleaming silvery surface. It could be used for any number of purposes, especially in the hands of a master smith, but it glows with a curious magic, rarely seen in these parts... Item 'the robot's control panel' is type orb, with keywords 'robots control panel torn out remains automaton'. The robot's control panel is in excellent condition. Has 5 of 5 total charges of level 240 spell 'force field'. *This item may be repaired 5 times. Odd electrical circuitry tangles its way in and out of a seemingly endless number of sockets and ports within this panel, exhibiting the great skill and aptitude for the disciple of its creator. Almost a shame that the robot had to meet such an ignominious end, but for its omnidestructional desires. Or was that, especially because of? This item is beyond your power to identify further. Item 'an automaton's crossbow' is type weapon, alignment 0, made of steel, has keywords 'automatons crossbow bow robot destruction', equipped wielded as a weapon. This item weighs 0 stones and 60 pebbles, and is valued at 58,000 gp. This level 240 item has the attributes: identified insulated magic-resistant An automaton's crossbow is in fair shape. Weapon type is crossbow, does 198 points of lightbeam damage for 1 stamina, accuracy 15. With your knowledge of 'archery', this weapon can cause 249 damage against 0 ar. This item has 2 empty Relic bindings. Affects personality by -1. Affects saving-rod by 3. Affects courage by -2. Affects damage by 18. *Your proficiency in 'lore' must be equal to 100 to use this item. *Your proficiency in 'archery' must be greater than or equal to 80 to use this item. *This item may be repaired 17 times. This crossbow has been modified by unknown means to shoot pulses of light, at a very rapid rate. This rate is only maintainable with a significant electrical power supply, such as the one contained in the automaton that this weapon was broken off of. Without the power supply, this weapon cannot shoot as fast, but still does a fearsome amount of damage. Most people would never even know its true power, however, because as few have seen the mechanical beast that spawned the crossbow, fewer still have seen it without the covering normally shielding it, and would thus mistake the crossbow for a simple lantern or magical flare. Item 'the automaton's intelligence core' is type manual, alignment 0, made of steel, has keywords 'thick bundle copper coils capacitors automaton intelligence core'. This item weighs 0 stones and 80 pebbles, and is valued at 12,300 gp. This level 186 item has the attributes: identified unique The automaton's intelligence core is in excellent condition. This manual contains learning techniques that will alter knowledge of 'color spray' up to 5 points. *Your age must be greater than or equal to 22 to use this item. *Your natural proficiency in 'color spray' must be less than or equal to 70 to use this item. This dense, heavy, complicated device shows a remarkable level of craftsmanship. Tiny wires go in and out of everything! Its actual mechanism of is a total mystery, but it has demonstrably functioned. A little panel on the side of the largest cage has instructions, scrawled almost too small to read. Written in an illegible mix of gnomish and goblin, it appears to be instructions for operating some kind of light-based weapon, but beyond that, it's anyone's guess.