As someone who loves to use Venusaur, both mega and not-mega, in competitive and casual battles I can say this:
ChloroSaur will beat Zard due to outspeeding it and either KOing it or just sleeping it.
Normal Venusaurs can beat Charizard, but it requires more thought and tact. Unless you brought HP Rock for some reason, or used Stealth Rocks. This is because Venusaur is very specially bulky and Charizard is very specially strong so they'll typically 2HKO each other unless Saur manages to sleep Charizard or got a poison on sludge bomb.
Mega Venusaur will dominate Charizard X, and can 2HKO it with Earthquake with no investment (in fact part of why I use Quake on mine is for this reason, aside from letting me bait Tran in), but Charizard Y will basically auto-win against Mega Venusaur as it's so insanely strong that it can OHKO any Saur without good special def. investment and will 2HKO even the most specially bulky of Saurs. Meanwhile, Saur can only hope to OHKO with HP Rock (which is very unviable), and if it opted for a modest sp.attacker set in the first place to net that kill, Zard will one-shot it anyways meaning it's pointless. The only way Saur can hope to win is if it manages to land Sleep Power and then doesn't die to a very angry charizard if it wakes up. And considering that Zard-Y often carries roost these days, it'll be pretty moot in the long run.
As a guy who's gotten to the 1800s using a Mega Venusaur team I'm speaking from experience, so basically to sum it up:
>ChloroSaur beats Zard
>NormalSaur is evenly matched against NormalZard, and it can go either way
>MegaSaur beats Zard-X if it isn't set up, and can sometimes beat it anyways if it's at only +1
>Zard-Y steamrolls MegaSaur and will absolutely incinerate it's health, even if it's no longer weak to it, because Drought makes up for that loss
Overall I'm pretty pleased that my boi is doing so good. I'm proud of how far Saur has come.
>Using Blastoise
