Showdown autosets your EVs to 252 in everything in Custom Game and related formats if they are all 0. You can confirm this using the !showteam command or checking in battle stats.I noticed a weird discrepancy between the calculator and actual damage hits on Showdown.
I was testing Freeze-Dry's interaction with Tinted Lens on a Water/Steel type in https://replay.pokemonshowdown.com/gen8customgame-1404538578, and I got this damage roll (this Kyurem doesn't have Tinted Lens, not that that should affect the damage roll anyways):
The opposing Kyurem used Freeze-Dry!
(Naviathan lost 31.5% of its health!)
However, putting in the same Pokemon into the calc, I get this:
0 SpA Kyurem Freeze-Dry vs. 0 HP / 0 SpD Naviathan: 135-159 (38.9 - 45.8%) -- guaranteed 3HKO
Both Pokemon were 31 IV, 0 EV, neutral nature, and level 100 in both the calc and on Showdown, so I don't understand where the discrepancy is coming from.
252 SpA Kyurem Freeze-Dry vs. 252 HP / 252 SpD Naviathan: 118-141 (28.7 - 34.3%) -- 4% chance to 3HKO