Once three or more creatures you control have attacked, you'll be given the option to discard a card at random, even if some or all of those attackers leave the battlefield before Gallia's triggered ability resolves
Blink spells make a commander leave, then return to the battlefield, which means a blink deck with Candlekeep Sage will draw two cards every time it flickers its commander
C Common Xyz Reborn X TRAP Target 1 Xyz Monster in your GY
Healing cards in general are primarily considered a waste of space for providing no direct field or card advantage
For example, there are around 114 cards in Blue and Green, and I have played all but 6
Traveling Chocobo would be great just with the doubling effect, but it comes with the added bonus of being able to play lands and cast Bird spells from the top of your library