Giratina ex : Giratina ex and Darkrai ex team with Greninja for a classic "good cards" deck build
Modern Masters is a glaring example, but even the event decks and clash packs are becoming regular value bombs
Loyal Three Normal/ex (Alt Arts) Pecharunt ex (Alt Art) Cassiopia (Alt Art) Earthen Vessel Competitive pulls: Pecharunt ex Okidogi ex Fezandipiti ex Crobat Binding Mochi Janine's Secret Art Cassiopia Xerosic's Machinations Ursaluna Dartrix Zoroark Powerglass Neutralization Zone (until Stellar Crown, and Area Zero takes over the format) Due to the set being relatively small, the pull rates should be pretty good
Ive played a lot of Yanmega ex in my Hydrapple ex build (which I used to get to Arceus League on Pokemon TCG Live), and can personally attest to how strong and reliable this attacker can be
Most top-tier price checkers offer tools that show you a card's sales history, market trends, and even population reports
#17 Vampire Nighthawk , and Figure of Destiny would be my choices