Don’t be serious if you can’t keep it up.
You know how lots of children’s cartoons don’t take themselves very seriously? They’re generally not allowed to, what with the slightest amount of seriousness damaging their minds and all that (puh-lease), but it also makes for a very cohesive experience. Playful art-style, simple dialogue, easily identifiable themes. It’s all on the same level which makes the ride really smooth.
But sometimes you get these shows that want to appear very mature and realistic. And that’s perfectly fine in its own right. What’s less okay is when they don’t keep the rest of their production up to that standard. You can’t just build an intricate world with complex characters and dynamic relations, and then throw in some piss-poor dialogue because “we need to explain this more” or something. It throws the entire look and feel they worked so hard on to shambles, because one of the elements just doesn’t hold up.
You can go the other way around with this, to an extent. A mostly silly show tacking complex issues in a light-hearted way can be great if you do it right, and it’s something we see a lot of cartoons these days do. They get away with it because there is no expectation of “realness”, so when they suddenly do turn that direction, its effect is even greater.
If your Mister Eevile explains his masterplan, that’s fine. If your calculating, legit-scary mob boss does, it’s not.