Doubling Season doubles the number of counters, so you'll put two lore counters rather than one
Trainer Gallery The set description for Brilliant Stars mentions that it contains a special Trainer Gallery subset of 30 cards with artwork featuring fan-favorite Trainers and Pokmon. With this and the very high count of Full Art rarity and higher cards from the Japanese set VMAX Climax in mind, not all of the special cards from VMAX Climax will appear in Brilliant Stars
Swampwalk is fine, definitely if with Urborg, Tomb of Yawgmoth on board
There are still plenty of targets for it, so no reason not to play it
Includes 1 Pokmon TCG: Sun & MoonCosmic Eclipse booster pack containing 10 cards and 1 basic Energy Customer will receive one of the 4 packs shown
Death-Greeter's Champion A 3-mana creature with double strike, support 1 for double strike, and a 4-mana dash cost