I guess this is a neat enough time to talk about creature types -- a lot of what we'd call 'player race' charcaters in D&D tend to have a type that corresponds to their species/race ('Zombie', in this case) and one that corresponds to their class ('Wizard', in this case)
With Flying and a 5/5 life counter, Shivan Dragon is able to wreak havoc on the opponents battlefield and, if left unchecked, ends matches in short order
We think this is teasing a new Team Rocket set.
Grades like GD+ work in an analogous way, however it usually only makes sense between Near Mint and Excellent, as nobody really cares if a card is LP+ or LP-
It makes it so much easier to get decent trainer cards, especially for newcomers!
It's a shame the amount of market share this legendary is getting now, but it makes sense due to how strong of a card it is and how it synergizes well with one of the strongest decks right out of Ursula's Return