What is the appropriate power level for a board made by a single card without normal summoning?

Windwitches can make an indestructible Crystal Wing. Terrortop leads to Zoodiac madness. Brilliant Fusion opens up a lot of plays. In your opinion, what should be the kind of board you can make with one card while preserving your normal summon?

I think that ending with a single quick effect destruction or negate is fine, as long as Maxx "C"-ing the start would draw at least 4, and it's hand trap disruptable. Two negates is a bit much since then there's no Kaiju out. I'd also prefer them not going any plus (so one card leads to net one monster on the field and one fewer cards in hand). There's probably a lot of factors I'm not thinking about though.