Menagerist/Guide

Introduction
Menagerist goblins are unique for a number of reasons:
 * There is absolutely no efficiency increase in farming them on any difficulty above Normal
 * The farming is finite, as 19 kills are required no matter what
 * Appearance rate is static and is estimated at 3.5% in place of any Treasure Goblin spawn
 * Note that while any normal open-world spawning point is valid (as long as it's in Adventure Mode), the following exceptions apply:
 * Cannot spawn from Bandit Shrines
 * Cannot spawn in The Vault

Preparation
Speedrunning the Normal difficulty areas appears to be most efficient method. Running through the selected zones, from end to end, one by one, then exiting to character selection and restarting the game will be the optimal solution, repeating dozens of times (assuming optimal statistical probabilities, about 18 resets per pet).

A build with maximized speed / relocation abilities is advised. An example of such build for the : Items that supplement it:
 * (Wind Shear supplementing generation if needed)
 * Bravado
 * Marathon
 * Ferocity
 * Pound of Flesh
 * Animosity and Unforgiving (to fuel Fury for Whirlwind)
 * Wrath of the Wastes Set
 * Bul-Kathos's Oath Set
 * Pride of Cassius to prolong Bravado
 * Chilanik's Chain if coupled with
 * Krelm's Buff Belt
 * / Obsidian Ring of the Zodiac (to keep the cooldowns minimal)

Locations
Most of the high-probability locations have been greatly nerfed by patch 2.6.6, but the following zones still have a decent chance (about 35% each) of spawning a Goblin, with a Menagerist appearing roughly every 30-35 kills on average: In addition, Core of Arreat, while nerfed significantly, only takes 20 seconds of running to cross with top-speed builds, so it can be added to any other route with ease.
 * Cave of the Moon Clan (both levels)
 * Western Channel and Eastern Channel (both levels of each)
 * Caverns of Frost (both levels)
 * Note that Icefall Caves have MUCH lower chances and are generally better off ignored

Tips

 * Do not go out of way to kill monsters or collect loot, as on Normal, it's not worth the reward
 * For the same reason, it may be wiser to ignore The Vault / Not The Cow Level / Whimsydale portals (unless farming for Cosmic Wings at the same time)
 * Most zones are single-Goblin spawn only, so no need to check every corner after a Goblin appears there
 * Zones with multiple levels are completely separate in terms of Goblin spawns: one can meet zero, one in either level, or two on two different levels in the same game. Therefore, check both levels.
 * To conserve time, it may be wise to ignore exploring every corner, if that would require too much backtracking, and move on to the next zone
 * Goblins can appear (although relatively rarely) in interim zones such as Southern Highlands or Fields of Slaughter on the way to the caves
 * Cave locations are chosen randomly from a fixed amount of spots, memorizing those can help locating them faster
 * Bounties can help locate relevant zones as well