Niv, Kykar and Dionus would already go great into decks I have. Shroofus could be fun to build around for mono g, which would be tougher than building Slimefoot.

Based on what I've played in 5E, I'd have to go with Wizard, but that's only because I've played two different flavors. I've only ever tried a Moon druid and I started a barbarian but had to drop out of the campaign after two sessions.