Game mechanics

Game Mechanics refers to any action that automatically happens due to the interior workings of the Yu-Gi-Oh! game.

Monster Cards and the Graveyard
Whenever a monster is destroyed, be it by battle, or via a card effect, it is always sent to the Graveyard, unless a card such as "Dimensional Fissure" or "Macro Cosmos" is in play.

Field Spell Cards
Whenever a Field Spell Card is in play, and another one is activated, the one that was on the field first is destroyed by Game Mechanics, since two Field Spell Cards cannot be in play at once.

If a Field Spell Card is active, and a new Field Spell Card is activated, and if activation of that card is chained to with a card that destroys it, like "Mystical Space Typhoon" or "Dust Tornado", the already-active Field Spell Card will remain on the field.

Equip Cards
Whenever the monster that an Equip Card is equipped to is destroyed, or removed from the field, the Equip Card is automatically destroyed and sent to the Graveyard, unless there is an effect present to prevent it.