An activated mana ability is one that adds mana as it resolves, doesn't have a target, and isn't a loyalty ability
Its hard enough to deal with a seven, eight, or nine-drop on the first or second turn, but to have to do so against the absolute best creature in their deck against you
Sometimes the cards are also slightly smaller, as they were trimmed to the correct weight
The most sought-after pulls are the ultra-rare cards, which can include powerful Pokmon V, VMAX, or VSTAR cards, stunning full-art cards with edge-to-edge illustrations, and the elusive secret rares
(They are also welcome to play it in their deck, if they want.) And keep an eye out for hustlers: there may be some dishonest people who try to fleece lucky Expeditioneers, particularly if the person who opens them is young