Lots of reviews mention janky interactions between Loki and other niche ice types, like Trap or Mythic. But Loki does have a more powerful, if equally unconventional, use in the current environment heavily featuring the conspiracy breakers (MKUltra, Black Orchestra, Paperclip). Because the runner's on-encounter effects (including on-encounter checks from the heap, such as bin breakers!) happen before the corp's on-encounter effects, the bin breakers will miss their timing window to install versus a Loki; it has no subtypes from the runner's perspective other than Bioroid when encountered. If, therefore, the corp elects for Loki to copy an ice type for which the runner does not have a breaker installed already, they will be unable to do anything about the subroutines, despite having the relevant breaker available in their heap. Unfortunately, for Loki to copy a piece of ice, that ice must already be rezzed, and the normal play pattern of Netrunner means the runner would have therefore encountered every type that Loki could copy at least once. But, how might the runner encounter Loki without having the relevant bin breaker installed?
There are a couple situations in which this can occur:
1) The runner previously encountered a kind of ice for which they did not have a relevant breaker at the time, and have not encountered that type again prior to encountering Loki. No guarantees that this will happen, but if the runner for example bounced off a Vanilla in the early game, they might not have tried to hit the Vanilla again before hitting Loki.
2) The runner has trashed a previously installed bin-breaker to make room for a new program. In this scenario, the runner make have encountered a Barrier on server 1, installed Paperclip, and then trashed it later to make space for an MKUltra when encountering a Sentry. Now, when they encounter Loki, Loki can counter that other rezzed barrier and be unbreakable. Not an especially common scenario.
3) The corp has rezzed ice by abnormal means, such that the runner may have never had an encounter with that ice type at all. There are numerous ways to do this, but I want to highlight the easiest and potentially most devastating way to do it in Standard: with Haas-Bioroid: Architects of Tomorrow. Imagine the following layout: the runner has not yet installed MKUltra, having not encountered any sentries -- non are rezzed. The runner then runs on a 3-ice deep server, with a rezzed bioroid on the outermost position, and two more unrezzed ice behind it. They pass the first bioroid; AoT triggers and the corp rezzes the innermost piece of ice, a sentry such as Ansel 1.0 or Tyr. The runner continues the runner, and the corp rezzes Loki in the middle position. None of their bin breakers can install on the Loki, and the Loki now copies that innermost bioroid, guaranteeing all the subs can fire. If it's a Tyr, that means 2 brain damage, a trashed card and 3 credits, and a hard ETR. Crucially, there is literally no way to circumvent this without hard-installing an MKUltra, using some form of ice destruction, or potentially using a boomerang to break the ETR so they can pass: with no other rezzed sentries, the runner has no way to encounter a sentry and get the install trigger for MKUltra.
I won't say that situation 3 makes Loki either a top-tier ice or that it happens with extreme consistency, but I have had multiple games as AoT where this combo has let me toast a rig! I've copied Ansel and Tyr before, but the best one was copying a Ravana 1.0 who then copied the same Tyr sub twice, trashing 2 installed runner cards and gaining the corp 6 credits. Could have also opted for 4 brain damage, which is like face-checking a Janus with no clicks left, except there's also a soft-ETR attached. Loki is a great and tricky piece of ice, only held back by its low strength.