This set looks great so far! Here are some of the cards that I noticed:
Alolan Raticate: Slap a Choice Band on it and that's 90 damage for no energy. The new Yanmega is here. Throw in a Salazzle line and some DeVo sprays and you two shot basically everything. FOR 0 ENERGY.
Alolan Muk-GX: Add in Raichu and Salazzle and you hit for 250 w/ Choice Band. Not to mention the +30 from Poison/Burn which makes Choice Band unnecessary. Even without Raichu you still hit for 210 between Poison/Burn and Choice Band. Also, 220HP is the highest on a Stage 1 GX so far. A GX attack that can both buy a turn to set up and power up the main attack. Not to mention its free! Great card.
Marshadow-GX: 150HP is a big setback, and Psychic weakness means a Choice Banded Garbodor one shots with Acid Spray, for pete's sake. However, this will be a great tech for alot of decks and Marshadow/Night March in Expanded will be busted.
Kingdra: This card is great! Magma's Base or the new Po Town and a promo Koko or two and you've got a pretty potent deck. Being a Stage 2, however, is an issue. Will be interesting to test when it comes out.
Po Town: When Magma's rotates, this will be the replacement for Drampa/Garbodor. Other than that, meh.
Mount Lunakila: A debuff to a card that was never that good anyways (Aqua's Base). No ty.
Simisear: Basically just a worse version of baby Volcanion. May see some limited play after baby Volc rotates however.
The secret rares: Loving the artwork here! My personal favorites are Alolan Muk, Gardevoir, and Golisopod.
Everything else: Set filler. Inbefore they drop the best card of the set after I post this
Also, will Po Town work if someone were to use Rare Candy?