Chansey has an 11% crit rate
Let's run some numbers.
Oh damn, Ice Beam actually does 27.5%! I was under the impression it did. 18% I must have had my opponent's chansey with -1 Special from a previous Chansey Calc.
I actually was running Psychic Snorlax, so I had made a Psychic Spdef Drop into Body Slam combo, since we were both paralyzed. That in itself made worth it the jankiness of using Psychic Snorlax, and dozens of other Janks I was running with those experimental teams. Yo just gotta jank sometimes, it's worth the ELO expenditure, and in the long run you'll probably just regain it. (However ELO in non stochastic games does not have as much elasticity as it does in deterministic games, one can probably say they reach asymptotically their "true elo"if we define true elo as the elo one has when he goes sweat mode. However sweat mode itself is not sustainable so the "true elo" includes the capacity and consistency to stay in sweat mode and....)
So this is a 4HKO basically.
Let's assume an ex-paralized tauros (Healthy with low speed (actually we should assume a probabilistic model of Tauros, since he may be or may not be with a dropped speed, and this speed is independent of the also-probabilistic accuracy-component-of-paralysis)) Tauros.
We can simplify our modelling of speed and eliminate off-by-one errors in this variable, by defining that either player might go first, i.e: a speed tie. For matters of probabilistic branching calculations, the procedure shall be the same as if we were against a gengar.
We may adjust the calculation, as we would if this were any other event with %-precision probability, like a crit chance. In which case it is recommendable to go with 3/4ths and 1/4ths so as to simplify calculations. Whether in favour of paralysis or not, now depends moreso on your game style,
I for example would use 3/4ths, as I would prefer to get my tauros paralyzed for style points, as well as to take advantage of a subversion of expectations in terms of 4th move uncertainty. For we must consider also the advantages that mainline variants get by using alternative movesets ( blizzard tauros vs non-rest tauros in this case, but also applies to tbolt tauros vs cloyster/reflax (only other signficiant use of blizzard?).)
So 4HKO, let's define rests as a move that heals to full health, at the cost of 3 turns, instead of 1. Speed is mostly irrelevant in this case, as rest marks the start of the cycle. It only impacts in scenarios where switch out options exist and are relevant, which usually doesn't allow playing out to a full rest cycle anyways.
This locks tauros in a full cycle of resting, which of course assuming freeze chances and crit chances, means that chancey is bound to get a kill eventually.
But if chansey is paralyzed, this gives chansey an average of (3/4*3=) 2 attacks and 1 quarter, we may multiply this again by crit chance to get a more precise estimate, but this doesn't greatly change matters I think, especially considering Tauros can farm re-rests to reset the cycle until he gets a luckier roll. In this scenario, Tauros wants to move last, as you have one extra turn of information to consider whether to rerest or not, said another way, it would the turn advantage here is worth a chancey crit chance (11%) * a tauros. (funnily enough, the older generations are one of the few metas where variable-pokemon values, (like in chess where a queen is worth 9 but a knight is worth 3) are so relevant.
At any rate this would give tauros an extra attack to play with, where he can farm for crits or chansey paras. In which case chansey would have a chance at the Matchup by crit, instead of outright losing 100% of the time.
That said, chancey can still reapply thunder wave after resting in order to regain a chance. However chancey increases its own probabilities of being losing by paralysis, so probably no effect.
So yeah, Tauros pretty much beats paralyzed Chancey, but not non para chansey, exactly how much? At least 3/4ths to 1/4ths, probably by even more.
I mean non rest tauros also beats chancey, probably with a higher probability, the difference may only be marginal, but the difference is that rest tauros ends up non paralyzed, albeit with low health. Which will equaty to at least a Body Slam worth of damage (usually 30%), plus a paralysis chance vs non-norms, or Hbeam beam damage (55% usually) , a Hbeam + crit chance(22%* 1mon) , or an HBeam sweep (a win).
That's why chancey is the queen of Gen 1. Because it's all about chances!
