Gambler materia is a 
Command Materia in Final Fantasy VII Rebirth. Its ability, Gamble, picks a random ability or spell from the frontline party's currently equipped materia. Gamble costs 1 ATB charge to use.
Gambler materia has somewhat a similar role to Mime from the original Final Fantasy VII, which repeated the last action of a party member. Gambler is a job in certain Final Fantasy games; in the Final Fantasy VII series this trait is associated with Cait Sith.
Obtained[]
Gambler materia is rewarded for completing "Can't Stop, Won't Stop" odd job at the Gold Saucer, available after completing all other odd jobs.
Stats[]
| Level | AP required | Effect |
|---|---|---|
| 1 | 0 | Use Gamble |
| 2 | 300 | Use Gamble; MP costs of spells reduced by 25% |
| 3 | 600 | Use Gamble; MP costs of spells reduced by 50% |
Use[]
Gamble will randomly use one of the abilities of spells from any materia the party have equipped. It will not use a party member's unique abilities or their weapon abilities, and spells will still consume that spell's MP cost (albeit at a reduced rate at higher levels). Equipping a magic materia paired with 
Magic Efficiency Materia will further lower the MP cost when equipped to the character with Gambler; pairing command and magic materia with support materia (such as HP Absorption Materia) to the character with Gamble will allow them to benefit from the additional effects, but support materia on an ally's loadout will not be activated for the character using Gamble. However, magnify will never trigger with Gamble, and neither does 
Reraise or Spare Change. Gambler will only use the default spell in magic materia, but all known enemy skills can be used at random.
Gambler materia is risky, but has a few small uses. In cases where the party has a limited number of 
Magic Materia or Command Materia, most of their slots occupied by 
Complete Materia and Support Materia, Gamble can be manipulated to use one of those very few abilities. For rare materia, such as Comet Materia, Gamble is the only way for multiple party members to use the ability. Additionally, Gamble can use the abilities and spells of otherwise KO'd party members, and only consume 1 ATB even for abilities that usually require two, like Prayer, Jump, and Limit Siphon.
ATB Boost can be used with Gamble, but it costs 1 ATB charge to use Gamble, whereas ATB Boost normally only costs by starting a cooldown. Using another character's ATB Boost via Gamble does not use up their cooldown, but does add a cooldown to the character using Gamble before ATB Boost can be repeated.
Gamble itself has a short animation, but the ability gambled to be used has the same cast time as the ability normally would have when used without Gamble.