This set was a combination of Jungle and Base Set. Wizards of the Coast usually performs these sorts of reprintings with their card games, and the Pokémon TCG was of no exception. At the time this proved to be an unpopular decision between fans and players. Legendary Collection, which was essentially a "Base Set 3", on the other hand, was widely accepted by players and fans.
The combination of both Base and Jungle would produce 166 cards (150 not counting holo/non holo versions of the same card), so some cards were not included:
The "starry" holographic design used in the previous three English sets was rejected in favor of the "cosmo" design used in the Japanese sets. The design has remained in use since.
The glass beads used as damage counters in previous Theme Decks were replaced by cardboard counters with "10" marked on them in this set. This removed any confusion over what color bead represented what damage and was more cost-effective for Wizards to produce. The cardboard counters have remained in use since.