Ye Olde Inn

Can the expansion pack cards, heroes and extras be used in the main game quest the original game or are they centric to the addon quests and game only. I played in the 90s and have just bought the 2021 version so I have lots of questions.

Do the expansions add new mechanics make things more advanced/complex?

Each Quest Pack levels stuff up and adds more content. This is why it is good to play them in order. It also adds more interesting twists for seasoned veterans to keep them from getting bored. I wouldn’t add stuff in until I reached that specific Quest Pack and then allow it moving forward.

J_dean80 is right! If you add the extra cards to the original game you will kill the feeling of finding new contant when playing the new quest packs.
Also some items are intended to be used exclusively with specific scenarios: Snowshoes of Speed in snow/ice terrain while Elven Bow of Vindication is a relic of the Elven realm and must be returned to the Queen at the end of the quest pack.

The other heroes you can use whenever you would like, such as the mythic tier heroes, or the Knight and Rogue hero packs. These heroes are not really tied to any expansion. The exceptions are the lazy introduction of the Bard character in the Spirit Queen’s Torment, and the up and coming Rise of the Dread Moon expansion for the Knight.

Switching out some of the original heroes with the new ones can add some variety for veteran players without flooding the game with a lot of new stuff at once.