This is the worst-affected family, and Pokémon is the worst-affected series in the hobby.

The screw test

The Game Boy line splits, and the split is easy to get wrong. Game Boy and Game Boy Color cartridges use a 3.8mm gamebit (the same security bit as NES, SNES and N64). Only Game Boy Advance cartridges use tri-wing (tri-point Y0). If you brought the wrong bit, the answer is that you brought the wrong bit; it isn't evidence about the cartridge.

On any of the three, a Phillips screw means a repro or a cart that has been opened. Because both gamebits and tri-wing drivers are cheap and widely available now, this test is weaker than it used to be, but it still catches the low-effort fakes.

Label tells: the strongest single check on GBA Pokémon

Genuine GBA Pokémon labels (Ruby, Sapphire, Emerald, FireRed, LeafGreen) use a prismatic/holographic foil with a specific pattern that shifts as you tilt it. Counterfeits either use a flat printed label with a fake "sparkle" texture, a hologram with the wrong pattern or grain direction, or a foil that looks correct straight-on but doesn't shift properly under angled light. Compare against a known genuine copy under a single point light source and rotate the cart.

Across the whole Game Boy line:

• Genuine labels are precisely die-cut and sit flush.
• The Nintendo Seal of Quality is a reliable printing-quality test.
• GBC "dual-mode" cartridges (playable on GB and GBC) have a distinct clear/black shell. Verify the shell type matches the title's documented release.

Shell tells

• Genuine GB/GBC/GBA shells have "Nintendo" and a part number molded on the back, plus a date code.
• GBA shells should have the correct notch profile. GBA carts are keyed differently from GB/GBC.
• On GBA, hold the cart to light: genuine translucent-shell variants (like some Pokémon releases) have specific tint and clarity.

Board tells

Prefixes by platform: DMG- (Game Boy), CGB- (Game Boy Color), AGB- (Game Boy Advance). Mask ROMs carry Nintendo markings.

• Save hardware. Ruby, Sapphire, and Emerald contain an internal CR1616 battery for the real-time clock (berries, tides, Shoal Cave). A genuine copy has one; a fake usually does not, or has a hand-soldered substitute. FireRed and LeafGreen have no RTC battery, so a battery present on those is itself a flag.
• Flash chips. Fake GBA carts almost universally use generic flash (often 32MB flash mapped for multi-game bootlegs) rather than Nintendo mask ROM.
• Solder quality. Genuine boards are cleanly reflowed. Fakes show hand-soldered joints, especially at the battery and cartridge edge.

In-game behavior tests (GBA Pokémon specifically)

• RTC test. On genuine Ruby/Sapphire/Emerald, berries grow and the clock advances in real time. On a battery-less fake, the clock is frozen and the game may display a "The internal battery has run dry" message on boot. Note that a genuine cart with a dead battery shows this too, so it isn't conclusive by itself.
• Save test. Save, power off completely, wait a minute, power on. Fakes lose saves.
• Language and text glitches. Bootleg ROMs are often modified, badly translated, or region-mismatched. Odd capitalization, missing accents, or text overflowing dialogue boxes are strong signs.
• Mystery Gift / link features. Fakes commonly fail link cable and trading functions.

Most commonly faked titles

Every mainline Pokémon release on GB/GBC/GBA, plus:

• Mother 3
• The Legend of Zelda: Oracle of Ages/Seasons
• Fire Emblem: The Sacred Stones
• Final Fantasy Tactics Advance
• Golden Sun
• Metroid Fusion / Zero Mission
• Mega Man Zero series
• Rhythm Tengoku
• Card e-Reader material