Most importantly, the 2006 EX Dragon Frontiers set had a low print run due to Pokmon TCG's losing some of its popularity at the time
There was another with him dressed as Luigi, which is a high value card but manages to miss out on our list
The other consideration here is just how much value you are getting from discarding the card and whether a deck cares enough about discarding to play cards whose primary purpose is to be discarded for value
Lucario's popularity is a large part of the reason why Melmetal's cards can maintain positive momentum without any new reasons to enjoy Melmetal
(Some of them would take up more room than we have in the text box by themselves, but you probably won't control that many lands.) In case you do end up with more than 31 lands, the remaining prime numbers below 100 are 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, and 97