Calm Nature
EV
's 252 SpD / 128 HP / 128 SpA
Item: Leftovers
Tera Type: Grass
-Spore
-Substitute
-Leech Seed
-Giga Drain
Basically, I have been destroying teams with this build. The only real realistic counters, are multi hit moves. Maushold and Population Bomb especially.
If you don't stop Spore, you typically end up in an infinite loop. Setting up Toxic Spikes beforehand can make this all the worse. This is a setup where, it has to be taken right away or it's over.
Giving up the Ground STAB was not ideal, but after over 100 battles with this, I can say it hardly ever matters.
I wanted to contribute this. Been reading Smogon for many years, you all do a great service for Pokemon players everywhere. Thank you!