Egg determination glitch

Miscellaneous glitches of Pokémon Diamond and Pearl, Pokémon Platinum, and Pokémon HeartGold and SoulSilver

Exclusive to Diamond and Pearl:
Battle Barry every day | Broken escalator glitch (Japanese only) | Choice Banded Pursuit glitch (Japanese only) | Choice Banded U-Turn glitch (Japanese only) | Dress up Hiker glitch | Egg determination glitch | Fake Tower Tycoon glitch | Honey/Sweet Scent shop glitch | Mute Route 214 glitch | Mute Sendoff Spring glitch | Protect oversight

Exclusive to Platinum:
Ace Trainer battle loop (Japanese only) | Giratina Origin Forme glitch | Trapping Ability flee glitch

Exclusive to HeartGold and SoulSilver:
Boulder push glitch | Water stream glitch | Floating walking Pokémon glitch (poison variation, menu variation) | Sequence breaking

In various or all entries:
Acid Rain glitch (Platinum/HeartGold/SoulSilver) | Grass glitch (Diamond/Pearl/Platinum) | Global Trade System glitches | Incorrect sprite for the Defog HM (Diamond/Pearl/Platinum) | Pal Park daily limit oversight | Pal Park nickname glitch | Route 224 tile oversight (Diamond/Pearl/Platinum) | VS Recorder audio glitch

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Viewing a Starly Egg's nature (Careful) before it hatches.

Bulbapedia also has an article about Egg determination glitch.

PRAMA Initiative a également une page sur Egg determination glitch.

The Egg determination glitch, also known as the Egg nature glitch is a glitch in Pokémon Diamond and Pearl, which allows the player to check the details of the contents of an Egg before hatching it.

To perform the glitch, place an Egg in one spot of one PC box and a Pokémon in the same spot of an adjacent box. Afterwards, scrolling to the next/previous box with the L and R buttons will allow the player to very briefly view the held item, nature, ability or type of the Pokémon inside.

YouTube video by Wooggle Smith