The unset teletrap and key usually pops on the same mobs, with the unset teletrap popping more often than the key, and its not a 100% drop on the teletrap either, so it might take some time to get both items. The mobs that drop these items include some mob in Vir (never killed that mob), Pynai and a covert special operations agent.
Pynai is located in Eanoss Azelmar and the covert special operations agent is found in Cavhfail. The method to get to Pynai is shown in the guide for Mark of Ingress, so I would only show how to get to the covert special operations agent in Cavhfail.
Covert Special Operations Agent:
After entering Cavhfail, head northwards all the way through to reach a down. Upon going down, there would be a sw and se exit, go one room sw and there would be a covert special operations agent. Kill this particular agent, and he is not known to wander, so you would only need to camp that particular agent, but kill the rest if you want. This agent drops unset teletraps often, with a lower chance of dropping the key.
Entering Kezathin's Area:
The no-regen CPK area that combat will be taking place would be entirely no-trap and indoors, but the area before it (that is also no-regen CPK) is not no-trap, and either way, mixes can be used, so cure light and HE mixes may be made beforehand. Also, I have learned that wearing sp-cost-reducing items (mights or a dragon breath bracer) and casting fountain greatly increases the amount of time that you can last.
After wearing HP and SP equipment, spelling up and trunking all other stuff you would not want to lose, you would be ready to enter the area. Wear the teletrap and time it such that you use it just after a tick, it would buy you the maximum amount of time to move, as you will be transported to a non-pk deathtrap. After using the teletrap, search and when a northeast exit appears, with the black metal key in your inventory, unlock the northeast door, open it and move northeast into the no-regen CPK room.
Area before Kezathin:
This area is 4 rooms wide, with only west and east exits. Upon coming out of the deathtrap, there would be one room to the east, where there is a gate to enter to get to the main area where Kezathin is. Two rooms west from the deathtrap exit is the room where you would use to leave the area, by going up into a non-pk room in Unseelie. This is also a one-way exit, so use it only when sure. This exit room is also the room that you would pop in when you enter the gate that is in Kezathin's main area.
Kezathin's Main Area:
After entering the gate, you would be transported into a room with a similar gate, this gate is the gate that you would enter to leave his area, and is the only way out. Kezathin's area is a 25-room area (5X5), with Kezathin himself being right in the middle of it. You would need to trigger Kezathin by entering his room (move 2 north and 2 west from the gate) and he would speak something about intruders and asking you to "be gone". Then he would start making bombs that move around the 25-room area, randomly stop, tick down twice, and explode, dealing damage (1.5-2k+) to every player or NPC in the room. If the bombs made by him explode in his room, they do not damage him.
There are automatons in the area that would aggro you, but they don't hit very hard and die before their entire life is up. Upon their death, they become a bob-omb. Unlike bob-ombs made by Kezathin, these are stationary and if an automaton dies in the room, you know that the bob-omb it turns into will explode soon too. Bob-ombs from automatons' death that explode in Kezathin's room are ones that will actually damage him. So this is a game of waiting until automatons appear in Kezathin's room, kill them or wait for them to die from other bob-ombs that explode and wait for the subsequent automaton-made bob-ombs to explode until Kezathin produces a "yowl" that can be heard in the entire castle. Each bomb is unique, and one bomb blowing up in a room with a few other bombs does not mean that the rest would blow up also.
Once an automaton dies, another one would pop up simultaneously in the area, and all automatons are stationary, but can be spooked only with a donation mask. Once an automaton pops in Kezathin's room, killing it would cause its bomb to explode in that room, dealing definite damage to Kezathin. Kezathin has been known to die after about 13 yowls or so, so this run would drag on for some time, unless really lucky.
As the deathtrap door does not lock on normal repop (it takes a little while longer, probably 2-3 standard repops), this means that if you die, you may be able to get back quickly enough without requiring another key, but this also means CPKers like Kurik can get to you quickly, and as mixes can be used in the entire area, you should be extra careful.
When Kezathin dies, there is no special string throughout the castle, and he would die like a normal mob, but you would not be able to predict when as he would always appear "in good health". Upon death, you would be able to loot all the items that appeared on him, as none of them are vis-death. His repop time is also about 15-30 mins long, so you may consider to get out of the area (1 room up after entering the gate from Kezathin's main area) and camp for a new key for a second pop.
Looting the clipboard will grant boss kill.
You take Kezathin's clipboard. Kezathin's clipboard emits a bright flare of white light as it binds with you. You have killed a new boss, Kezathin, the mad tinker. You gain 25 practices! You have killed 7 bosses since your last PK.
Items that he may drop include:
Item 'Kezathin's clipboard' is type treasure, alignment 400, made of paper (in (new) condition), has keywords 'kezathins hardbacked wooden clipboard board notes'. This item weighs 0 stones and 10 pebbles, and is valued at 46,000 gold. This level 220 item has the attributes: identified unbreakable bind-on-take Affects knowledge by 4. *This item may be repaired 8 times. Kezathin writes down all of his best ideas on this clipboard. His southpaw scrawl darts along the page in an almost illegible line, no doubt readable to his trained eye, but foreign to others. There is a distinct lack of diagrams for a man who spends his time machining robots, but if he is well- organized enough to make what he does without them, more power to him. +++ Kezathin's clipboard will, when USEd, grant to its wearer the mark of Creativity. Item 'spring-loaded boots' is type armor, alignment 400, made of unknown (in (new) condition), has keywords 'pair boots springloaded strange material loaded', equipped on the feet. This item weighs 0 stones and 20 pebbles, and is valued at 54,800 gold. This level 240 item has the attributes: identified insulated wont-fuse unbreakable will-float Armor resistance is 11 pierce, 11 bash, 11 slash, and 11 exotic. This item has 1 empty Relic binding. Affects stamina-regen by 3. Affects stamina by 50. *Your Creativity must be equal to True to use this item. *Your stamina must be greater than or equal to 1500 to use this item. *This item may be repaired 5 times. The springs jut out of these boots from every angle, making stabbing oneself in the ankle a definite danger. Despite the perilous probability of puncturing, these boots look like their benefits outweigh their risks, offering a longer gait, and easier traveling. Item 'Kezathin's toolbelt' is type clothing, alignment 300, made of leather (in (new) condition), has keywords 'kezathins tinkers toolbelt belt', equipped around the waist. This item weighs 0 stones and 22 pebbles, and is valued at 46,000 gold. This level 220 item has the attributes: identified insulated bind-on-take This item has 1 empty Relic binding. Relic(s) bound to this item: a scale of the Kraken Affects knowledge by 2. Affects saving-petri by 1. *Your Creativity must be equal to True to use this item. *Your wisdom must be greater than or equal to 19 to use this item. *This item may be repaired 8 times. This toolbelt is held together by the strong leather thongs that make it so valuable. It can be used to hold almost anything, and knowing Kezathin, at some point, it probably has. Pockets and compartments of all size and nature cover its surface, which wraps its way around the waist, allowing for all sorts of additions and attachments.