They're all flexible and can fit in most decks of those colors, however, you have to cast them with mana in order to get their abilities, which is why they're lower on this list than they could be
Neon Dynastys Legendary Dragons Kura, the Boundless Sky Kairi, the Swirling Sky Junji, the Midnight Sky Ao, the Dawn Sky Atsushi, the Blazing Sky The original Kamigawa had legendary spirit dragons that, for a long time, were Constructed playable and even good commanders
The ceiling for goad is more than a 2-for-1: its a way to strip opponents of their board, their life totals, and the resources in their hand
While these principles or similar concepts can be applied to Constructed as well, were mostly just going to be discussing Limited here