I finally have Sandslash registered in my Pokédex ! It may seem extremely strange that I didn't have Sandslash yet, and I do agree with that. The main reason for this is that I prefer catching Pokémon in the wild or optionally from Raids in order to get them registered in my Pokédex. This makes it much more awesome compared to evolving them.
There was once a time long ago where I tried to do a Sandslash Raid. I was still level 29 back then I believe and I saw a Sandslash Raid that was still there for a few minutes. As I still had a free Raid Pass I decided to give it a try. I fought really hard and I was able to deal a good amount of damage to the Sandslash, but I only damaged it for about 95% or so of its health. I would've tried powering up some of my Pokémon like my Vaporeon, but the raid was gone by the time my fight was over so that was not a possibility. I had not seen any Sandslash in the wild since then, or was unable to go get them due to time.
As I defeated Giovanni using my quest from January, I was able to start the February Team GO Rocket quest. The step to spin 10 Pokéstops gives an encounter as a reward. When I completed it I was pleasantly surprised when this encounter turned out to be a Sandslash! This doesn't surprise me, because February's Shadow encounter with Giovanni is Raikou who is weak to Ground-type attacks.
Today the Pokémon Day celebration event went live too, one day before the actual Pokémon Day. As Pokémon Day happens on February 27 due to the first games in Japan being launched on February 27, 1996. This event also celebrates the Pokémon: Mewtwo Strikes Back - Evolution movie on Netflix on February 27. A lot of the Pokémon featured in the movie are now also spawning much more in the wild.
When I was walking around earlier today I randomly encountered a wild Sandslash! I was quite surprised because I already caught this Sandslash from the Quest reward to register it in my Pokédex and now I came across a wild one too! A bit later in the evening I went outside again for the weekly Raid Hour to do a few Armored Mewtwo Raids with some others. Between walking from one Raid to another I was able to encounter 3 more Sandslash! I took screenshots of all 4 of them which you can see here.
It kinda looks like now that I finally have Sandslash registered in my Pokédex I can suddenly encounter it more in the wild, but I know that their spawn rate has been increased as part of the event just like many other Pokémon.