>>47099285Corviknight, Zapdos, Skarmory, Moltres, Dragonite, Mandibuzz, Celesteela, just to name a few. All of which can maul Rilla back with STAB or punish him for trying to hit them.
Ferrothorn can take a +2 Drain Punch but does die to Superpower, and can hit Rilla back hard with Gyroball. Melmetal just fucking dunks it if it tries to take it out. It also loses to Scizor, Klefki, defensive Heatran if it’s not running HHP, and Kartana if it lacks Superpower.
Dragons who beat Rillaboom include Hydreigon (who I’ve personally used to great effect against him so I know from experience, though he can’t switch in on a boosted fighting move), aforementioned Dragonite, Salamence, Kyurem, Goodra and especially Kommo-o. Dragapult and Dracozolt can also win, the former with many tools to cripple/kill Rilla.
It also gets bodied by Clef/Pex unless it’s choice band (in which case it gets fucked by one of the above even harder).
Venusaur can’t beat every single one of those either but under sun he’s capable of beating a LOT of them.
Again Rillaboom in general is more reliable but don’t discard Venusaur just because sun isn’t super popular an archetype. He’s the best Chlorophyll user in the game for a reason.