As well as the rarity symbol on the card, the rarity of a Lorcana card is also indicated by the colour of the icon
If Dour-Port Mage leaves the battlefield at the same time one or more other creatures you control leave the battlefield without dying, its first ability will still trigger
Sunscourge Champion is really cool, as it fits into a lot of different strategies, providing two appropriately costed bodies for more aggressive strategies, good blockers plus lifegain for defensive lists and discard for decks that care about it
As most goblin decks are running 30+ goblins you can guarantee Ringleader is going to pay off and draw you at least 2 cards
He arrives with plenty of loyalty counters, he can lock down your opponent for a few turns, and if left to scry and draw cards, you'll wind up with an emblem that will almost certainly win you the game