Book of Vile Darkness 3.5
By Monte Cook
At one point during the duration of this spell, the caster can alter the probability of a game of chance. This spell can only affect nonmagical games, such as those using cards or dice. It cannot affect a game involving magic, nor a magic item involved in a game of chance (such as a deck of many things). Whenever a roll is made to determine the outcome of the game, the caster may force a reroll of the outcome and take the better of the two rolls.
For example, Darkon is playing a game called dragonscales, which he has a 1 in 4 chance of winning. The DM secretly rolls 1d4 and tells the player that Darkon lost. Darkon, under the effect of a cheat spell, can have the DM reroll. The spell alters probability, so there is no subterfuge that another character could notice (except for the casting of the spell itself ). To even an astute observer, it appears that the caster is just lucky.
Focus: A pair of dice made from human bones.