First of all, I want to point out that Revelation Dance is
not in the game (since Oricorio is not in the game) unselectable in the game, so it's not an option for Color Change.
EDIT: Wording changed slightly to be more accurate.
Also, because I can't leave this well enough alone:
To me, pumping the attack/speed stats to negate Slow Start feels different from going any other route, including the bulky offensive route. They are all ways of trying to work around the Slow Start drops, but I think the sticking point for me is that this route doesn't particularly engage the ability so much as it treats it as a little bonus. The threat of a sudden offensive boost feels lessened when the Pokemon is already strong enough to be an offensive threat on its own. To run some more numbers (assuming 31 IVs), base 240 uninvested is equivalent to base 111 uninvested, and 240 fully invested is equivalent to base 95 fully invested. Not great, but at this point you're just working with a typical (if perhaps weaker than usual) setup sweeper. Maybe I am being swayed too much by how high the stats need to be to reach "useful during Slow Start" levels, though (240, or really anything in the 200s, is absurdly high for any kind of stat, even accounting for legendary stat spreads). I won't deny that it's technically a unique niche (Slow Start is unhazeable to boot), I'm just not convinced this is the way to go for Slow Start.
Emergency Exit
What methods are available for us to safely get to 50% HP or lower?
I'm going to start by pasting a relevant phrase from
Bulbapedia:
"Emergency Exit will not activate if the Pokémon's HP falls below half due to hurting itself in confusion, Pain Split, or using Substitute or Belly Drum or Curse, but it will activate if the HP falls below half from all other damage (including Struggle recoil)."
This means that, while things like Substitute are off the table, we have the choice of activating Emergency Exit ourselves using recoil moves. Some moves directly hit the 50% threshold from full health, but there are also plenty of high-power recoil moves that we could use, even if they are less predictable in the amount of damage dealt to us. There's also Focus Sash/Endure on a super frail mon, although the inability of a 1 HP mon to come back in if there are hazards up puts a damper on this. Otherwise, we're mostly at the mercy of the opponent, so we'll need to come in on either chip damage or predicted moves that will chunk but not kill.
How can we take advantage of being forced to switch out?
Emergency Exit could allow us to fulfill an interesting niche as a suicide lead that can do its job more than once. Instead of exploding, Destiny Bonding, or simply dying as fast as possible to get out of the way, Emergency Exit could be triggered to activate an early switch into the desired check, while the HP threshold being so high means that the mon could be able to come back in again at a later point. To build on the recoil point, we could also use it to get an offensive mon out of battle quickly (perhaps if it's choiced) and put in our check of choice. Another, even more niche use of this is that damaging pivoting moves fail to switch the user out if they trigger Emergency Exit, so one could send Emergency Exit Pokemon in, take a little chip damage, then get a safe switch in while denying the opponent their own switch.
Mimicry
How detrimental of an ability is Mimicry?
It's detrimental in terms of losing your typing and STAB, so how detrimental it is depends on how reliant on those traits you are. As an example, Galarian Stunfisk prefers to keep its typing, so being susceptible to terrain taking it away sucks for it. A mon with a wider movepool and better stats might not care nearly as much, but it would still an annoyance.
It is less detrimental than a similar ability in Color Change (which also involves losing your typing), since there's more in your control (you can set your own terrain, often without going extreme lengths to fit a setter on your team, and it is more obvious when terrain is going up than what kind of move your opponent is going to use). In cases where a terrain user isn't present, Mimicry is completely neutral, and those cases aren't uncommon in the current metagame.
I think Jewvia's comparison to Forecast is generally pretty fitting. However, I do think it's more detrimental than Forecast just because terrain is more prevalent in the current meta, mainly because its more frequently seen on individual Pokemon that are also really good. Tyranitar and Hippowdon exist as a standalone Pokemon, but they aren't quite on the level of Rillaboom and Tapu Fini (while Tapu Koko is somewhat comparable). This means that Mimicry is going to come into effect more often, and you have less control over your typing in general. However, this individuality also means that designing around this ability mainly involves designing how to play against those setters (rather than a playstyle as a whole).
Overall, I'd say that this ability is a net negative because you lose control of your typing, but I don't think it's a very strong detriment unless you are very dependent on typing and STAB.
How can we make this differently from any other terrain abuser and still benefit from it?
Mimicry's main appeal is that it is adaptable to any kind of terrain, so one route is to use the opponent's terrain against them. Terrain Pulse is probably the most fitting move for this kind of approach, since it will always get STAB from Mimicry under terrain, and we could include terrain-specific moves like Grassy Glide as well. However, this isn't effective in the face of the setters themselves, which makes it more difficult for us to abuse that terrain. Another option is to check or counter the setters themselves (like by carrying Poison coverage), but we will lose STAB, and the setters usually have a way of getting out and/or smacking us with at least neutral moves. We could just go with a generalist approach of not engaging with the terrain in our movepool and just using the typing, but that ignores the ability and doesn't seem to be in the spirit of the concept. Pairing with our own terrain setter is another option, although at that point it's mostly inferior to already-existing terrain abusers.