It's a matchup that I usually feel behind in, but that said, I've had success with viper's kiss main (stops monstrous and can go on an agent if desperate). Nykthos can help get you back into matches, I've been added more and more lately.
Sorry I'm new here so it won't be formatted just right. Love to get feedback on a golgari deck I've been running online. It does great against g/r, and big boros. Mono black has been a tougher match up, and I haven't run into u/w heroic or fast boros yet. It plays well, but seems like something is missing, and I'm not sure if I'm missing something or, if the cards aren't there yet.
4 Sylvan
4 Voyaging Satyr
4 Reaper of Wilds
4 Arbor Colussus
3 Nemesis
1 Hythonia
1 Nylea
Spells
4 Commune with Gods
4 Read the Bones
4 Hero's Downfall
2 Whip of Erebos
2 Temple of Mystery
3 Temple of Silence
1 Nykthos
11 Forest
9 swamp
4 Dark Betrayal
2 Hunt the Hunted
2 Mistcutter Hydra
1 Hythonia
4 Thoughtseize
2 Fade in Antiquity