Mega Venusaur now?
Every legendary except Articuno, Moltres, Zapdos, Raikou, Entei, Suicune, Regirock, Regice, Celebi, Registeel, Latias, Latios, Jirachi, Uxie, Mesprit, Azelf, Heatran, Cresselia, Shaymin, Manaphy, Tornadus, Thundurus, Landorus, Cobalion, Terrakion, Virizion and Keldeo is considered too overpowered to be catchable. And catching these is extremely hard, too. For the record, an League Official shall fight you with the legendary. It is a 1 Vs. 1 battle. If you beat the power of a League Official who is using a legendary, you automatically catch the Pokemon. But it is so difficult that a Camerupt lost to a Heatran despite having that 3x Type advantage. And the Camerupt user was a Gym Leader, too.
Choose an arena for your battle with Volcer. You can write one up, too. But please choose or create an interesting arena. I am bored of refereeing Lawn, Clay, etc.