The main way to obtain the Pokémon card (old back) "Mew Lv.23" is through its inclusion in the third expansion pack, "Fossil Secret," released in 1997. Mew Lv.23 ★ [Old Back] No. 151 "Fossil Secret" is a highly sought-after and rare card among the old backs, commanding a high price. It is especially sought after by collectors for its ★ (rare) mark and its "old back" design, which is an early Pokémon card.