This word search contains the names of thirty Pokémon from the first generation of games. The completed grid looks like this:
The leftover letters spell out the phrase FULLY-EVOLVED FORM OF MISSING THREE-STAGE EVOLUTION IN GEN ONE. In the first generation of Pokémon games, there are sixteen three-stage evolutionary lines, ranging from Bulbasaur-Ivysaur-Venusaur to Dratini-Dragonair-Dragonite. Each of the names hidden in the puzzle comes from one of these lines, and in fact, the thirty Pokémon consist of two Pokémon from each of fifteen of the sixteen evolutionary lines.
The one missing line which does not appear in the word search is Weedle-Kakuna-Beedrill. The fully-evolved Pokémon in this set is BEEDRILL.