Master Ball Holo
A Master Ball holo is a rare reverse-holo pattern of tiny Master Balls, introduced in the Japanese 151 set and reused in later Japanese sets.
The Master Ball holo is a special reverse-foil pattern where the card body shimmers with a repeating Master Ball design. It debuted in the Japanese Pokémon Card 151 (SV2a) set, where it replaced the standard reverse holo treatment alongside the more common Poké Ball pattern, and has returned in later Japanese sets.
Master Ball versions are dramatically scarcer than their Poké Ball counterparts, so a Master Ball print of a popular card — especially a starter or pikachu-line Pokémon — can be worth many times the regular version. A practical note: these patterns are a Japanese-set feature, so English 151 cards do not have them; check the language before buying.