Lock

Lock (呪縛ロック Rokku) is a keyword, introduced in Trial Deck 11: Star-vader Invasion.

“	You can't move; you can't attack; you can't even retire. All you can do is just float there.	”
—Suiko Tatsunagi, Episode 130

When a unit is locked, it turns face down, and remains face down in where it is until the end of its owner's turn (Known as a "locked card"). A locked card cannot be used to perform any action; it cannot attack, boost, intercept, use its own abilities, be used to pay costs, move to another circle or zone, or be retired by calling another unit over it. The locked card not considered a unit, and both it as its circle are considered to not exist while it is locked.

In the anime, this is visually shown as two rings collapsing onto the unit reverting it into card form and on the table, the face down unit is shown to emit sparks when a cardfighter attempts to touch it.

Unlock

All locked cards are turned face up at the beginning of the owner's end phase, this being called "Unlock" (解呪アンロック Anrokku). When a locked card is unlocked, it turns face up in [Stand] state, and any effect gained that it had before it was locked disappears.

Eg: If the unit would leave the circle at the end of turn, it would not happen since it was locked.

Also, the unlocked card is not considered to be placed on (RC) and thus "on-call effects" are not activated.

Introduced in Booster Set 14: Brilliant Strike are units that can unlock other units before the end phase, most notably Salvation Lion, Grand Ezel Scissors who unlocks all of his rear-guards with his Limit Break. This allows units to make their opponent's locking efforts nullified or to relock units to reuse locking skills.

Omega Lock

"Omega Lock" (Ω呪縛オメガロック Omega Rokku) is a special type of lock introduced in the Episode 156, which it prevents a locked card to be unlocked during the owner's end phase. Star-vader, "Omega" Glendios and Dark Zodiac can Omega Lock all of the opponent's locked cards, including current and future, during the next end phase. It is shown in the anime that is "Lock the Lock"

Frequently Asked Question

Question: If I have Liberator of the Round Table, Alfred as my vanguard and 1 of my 5 rear-guards has been locked, will my vanguard's Power be 19000 or 21000 due to his Limit Break?
Answer: 19000. Your locked card does not exist on the field anymore.
Question: If my vanguard is Dragonic Overlord and my only rear-guard is an Embodiment of Armor, Bahr which is locked, will my Dragonic Overlord gets [Power]-2000?
Answer: Yes. It will be treated as though there is not a unit on the rear-guard circle, meaning Dragonic Overlord will get [Power]-2000. Note that this does not affect skills such as Lord, since the locked card no longer counts as a unit.
Question: If the card text says that I may lock my own rear-guards instead of my opponent's, then do my locked rear-guards stay locked until the end of my opponent's turn?
Answer: No. If you are the one who locked your rear-guards then you will turn them face up at your end phase. If you lock your opponent's rear-guards, then your opponent must wait until the end of his/her next turn. Also, be noted that Prison Gate Star-vader, Palladium's skill allows you to bypass this ruling.
Question: If I have a locked card in one of my rear-guard circles and they no longer exist on the field can I retire it to place a new unit in it's place?
Answer: No. Though the card no longer exists on the field it cannot be retired because there would be nothing to retire. The idea is that the rear-guard circle the card is locked on is engulfed by the void. So a locked card cannot be retired to play a new one.
Question: If I unlocked my locked cards during my main phase, are they unlocked as rest or stand?
Answer: Stand.