Hammerspace

Hammerspace is a term used to refer to an invisible space where fictional characters can pull out objects larger than the physical space they are stored in. RPGs (Role-Playing Games) refer to this space as a Magic Satchel. In the Sonic continuity, many characters are seen pulling large objects out of nowhere (usually Chaos Emeralds). This can be considered as sort of a "video game logic" that has no real meaning to it and is not important to the story or gameplay, but can sometimes happen as an element of gameplay.

Users
Many characters have been seen having access to Hammerspace, such as:
 * Sonic the Hedgehog
 * Shadow the Hedgehog
 * Silver the Hedgehog
 * Amy Rose
 * Knuckles the Echidna
 * Miles "Tails" Prower
 * Dr. Eggman
 * Espio the Chameleon
 * Vector the Crocodile
 * Rouge the Bat
 * Bean the Dynamite
 * Chip

Usage in games
In games, characters are commonly seen pulling objects out of nowhere. This includes, but is not limited to, the following:

Sonic Adventure 2
In Sonic Adventure 2, Tails pulls a walkie-talkie out of thin air after beating Eggman.

Sonic Heroes
In the last story, after Eggman shouts about the Chaos Emeralds, several characters all pull out a Chaos Emerald, all seven in total, completely out of Hammerspace. Also, during gameplay, a few objects are pulled out of Hammerspace by certain characters:

Amy Rose
Amy can pull impossible amounts of Piko Piko Hammers out of Hammerspace.

Espio the Chameleon
Espio can pull an indefinite amount of ninja stars out of Hammerspace.

Big the Cat
Big can pull his fishing rod out of Hammerspace to attack enemies.

Vector the Crocodile
Vector can pull out an infinite amount of bubblegums to blow bubbles with (Team Chaotix's version of the Triangle Dive).

Shadow the Hedgehog
During Team Dark's Team Blast in Sonic Heroes, Shadow pulls a Chaos Emerald out of Hammerspace in order to perform Chaos Control, even if the other teams have all the Chaos Emeralds.

Sonic Battle
Several characters can pull objects out of Hammerspace when performing special attacks:
 * Sonic can pull out rings and explosives.
 * Tails can pull out boxing gloves, energy cannons, explosives and magic hands.
 * Knuckles can pull giant boulders out of the ground and can also pull out explosives.
 * Amy can pull out Piko Piko Hammers, explosives and boxing gloves.
 * Rouge can pull out large balloon-shaped objects.
 * Cream can pull out spade-like objects.
 * E-102 Chaos Gamma's Jet Booster will appear when activated and will disappear when Gamma hits the ground.
 * Emerl and Phi can pull out all of the above.
 * During most of these actions, the items in question usually appear from a "flash" as though they were teleported there.

Shadow the Hedgehog
In Shadow the Hedgehog, Shadow was shown having access to Hammerspace. He would often pull any Chaos Emeralds he had collected out of nowhere and then they would just vanish without any physical means of transporting them. In one scene, however, he made a gesture where he appeared to be putting two Chaos Emeralds in his "pockets" although he wears no clothing.

Also, the guns Shadow carries use Hammerspace, indicated by the fact that he never needs to reload them.

Sonic Riders
During gameplay, the character can pull out objects when boosting to attack others. For example, Wave can pull out a wrench or a stick of dynamite to attack. Jet stores his cube key and his Bashōsen in Hammerspace. Another example is Tails, as he pulls an electric wire out of nowhere while boosting. In Sonic Riders: Zero Gravity and Sonic Free Riders, the same thing happens.

Sonic the Hedgehog (2006)
Several characters pull Chaos Emeralds out of nowhere.

Sonic Chronicles: The Dark Brotherhood
In Sonic Chronicles: The Dark Brotherhood, the player is capable of collecting an indefinite amount of items, without any visible means of transporting them.

Sonic Unleashed
Chip is able to pull chocolate bars out of Hammerspace.

Subversions
A subversion (in this case) is when a character shows how they are able to pull out an item without the use of Hammerspace.
 * In one episode of Sonic X, Amy holds out her hand and a Piko Piko Hammer appears in a puff of smoke.
 * In another episode, it appears in a flash of light.
 * In the Sonic X comics, while trapped in Eggman's virtual world, Amy comments that she can't "feel" her hammers.
 * At some points in the Sonic the Hedgehog comic series, a number of characters (especially Knuckles in the earlier issues) would pull small items out of their gloves.
 * In one episode of Sonic X, Tails pulls out a Chaos Emerald from between his two tails.
 * Another episode of Sonic X shows Rouge pulling Bokkun's locket out of her chest.

Sailor Moon

 * Every time, Sailor Mercury takes out her Supercomputer of nowhere.
 * Sailor Moon pulls out the Moon Stick and the Cutie Moon Rod of hammerspace.

Pokémon

 * Characters pull Poké Balls out of nowhere to catch Pokémon.

Other Subversions

 * Cinderella pulls the Glass Slipper out from her apron.
 * Helga pulls a Flare pistol bullet out of her pants.
 * Little Hiawatha stores a spare bow and arrow in his pants.
 * Sailor Moon stores the Yellow Rainbow Crystal and the Moonstone in her leotard.
 * Similarly, Sailor Venus stores The Star of Astoroth and the Mirror of Incanta in her leotard.