The owner of a vanguard card is the player who started the game with it in the command zone
Attach auras and equipment to both creatures and they can deal even more damage to an opponent because of their ability, perhaps to the point of one-shotting them depending on their life total
It's extremely useful as it can be used to replicate a more expensive spell for just two mana
Estrids Invocation is particularly sweet here, since during each of your upkeeps you get an opportunity to exile it and bring it back to the battlefield, so if Jin-Gitaxias has transformed again, you can copy The Great Synthesis again
Sporting two formidable abilities on a two-drop, I think its is the best gold signpost uncommon in the set
So if you have ten Elves in play, Banner of Kinship gets ten counters, and they all get +10/+10