>>58689565M-Absol's been working fine for me, 80+130 is good for hitting the new hp thresholds. Absol's gets the most value in the early game, you should be using it to kill supports like Cyrus and Lillie and build your Hydra in the back to finish up, not the other way round. Also M-Absol having 1 retreat cost means Hydra can Roar and retreat if it needs to and Absol can come and attack, its flexible.
I can't really recommend other dark-type exs,
Darkrai is too slow to build and energy hungry, you can't attach energy to it when you're firing off Hyper Rays.
Weavile maybe but the damage is inconsistent.
Umbreon + Collect Eevee if you wanna have a bit more draw power and free Cyrus, but the retreat cost is high, though running it with regular umbreon can help you stall.
Crobat is hard to fit in because its another stage 2 line.
You kinda just have to play around the 1-1-3 point threshold when playing Megas
