What? Showdown fixed this a long time ago, they are doing it based on base HP.When a Pokemon uses Dynamax on Showdown, fractional HP transactions (heal pulse, leech seed, life orb, etc.) are based on the current (increased) HP stat of the Dynamaxed Pokemon. However in the games, these transactions are based on the HP stat of the Pokemon in its base form.
When we get to it, the last 5 days have been high priority interruption after high priority interruption. (Dynamic speed, priority breaking, switch speed order, and more). There is alot to fix and some things are more important than others please have patience.
1. pain split has been reported 5 times already.https://replay.pokemonshowdown.com/gen8randombattle-1022858927
couple of bugs
1) Pain splitting gives hp but doesnt reduces the opponents
2) jolteon for some reason not taking damage by spikes despite it being LO