Venasaur-Mega - Because this is Bold natured (especially considering Mega Venasaur’s attack stat is less than its special attack to begin with) Power Whip isn’t that good. It also has inconsistent accuracy. Giga Drain would be a good replacement. And if you do choose Giga Drain, then you can get rid of Synthesis for Sludge Bomb. HP Fire could be a consideration, but Leech Seed can be good, especially with Sleep Powder. Coverage is really good in monotype, so that’s definitely something to think about.
Breloom - Interesting set, but in my opinion, Technician Breloom is better than Poison Heal because it hits so much harder and Breloom isn’t really tanky enough to take advantage of Poison Heal anyways, plus it wastes an item slot. It’s sort of like giving a Greninja Leftovers. Here’s a standard Technician set in case you wanted to try it:
Breloom @ Focus Sash
Ability: Technician
Jolly Nature
EVs: 252 Spe/252 Atk/4 Def
- Spore
- Mach Punch
- Bullet Seed
- Rock Tomb
Technician boosts attacks with a base power of less than 60 by 50%, which is why I recommended Bullet Seed, even though it’s usually not a very competitive move. This is focused on being as fast as possible because of Spore, but if you’re going to rely on Mach Punch more you can make it Adamant. It has a Focus Sash, and hazards aren’t very popular right now, so I wouldn’t bother investing in HP, like your poison heal Breloom.
Cradily - I think this is fine. Just watch out for Taunt. I doubt your Rock Slide will do much.
Ferrothorn - Spikes aren’t that great now that a lot of Pokémon (like Cinderace) carry Heavy-Duty Boots. Power Whip is probably better. Rocky Helmet over Leftovers is something to consider, since you already have leech seed.
Rotom-Mow - This also seems fine. I think you made the right choice with choosing Scarf instead of Specs, but feel free to try Specs if you think you aren’t hitting hard enough.
