The combat mechanics of Doctor Who: Legacy involve matching colored gems in combination with the abilities of a team of characters. Combat is turn-based, allowing the player to take his or her time making a move. To make a move, the player selects one gem on the board and drags it around the board for a short period of time, swapping it with other gems as it moves.
Combos
A combo is a group of gems composed of horizontal and vertical line of three or more gems in a row. After the player makes a move, all combos on the board will be cleared away, and any characters on the player's team that match the color of the cleared gems will get an attack for the turn; if the cleared gems are pink, the player's team gains health based on its combined Heal attribute. If five or more gems are cleared in a single group, an attack will hit all enemies.
The strength of an attack for a given character is based on its ATK attribute. A group of three gems matching a character's color results in that character getting an attack strength equal to the character's ATK. Each additional gem cleared in a single group of gems adds 0.25 of the character's ATK to the attack strength. The same is true for healing, except it uses the team's combined Heal attribute instead of a character's ATK.
Multiple combos can be made in one turn, and new groups of gems that form when gems are replaced from other cleared groups of gems will be cleared away immediately. Each additional combo beyond the first in a single turn will add an 0.25 multiplier to the strength of each character's attack, as well as to the amount of health gained by matching pink gems.
Character powers
Character powers can be used to influence combat in the player's favor. Each companion's power can only be used after a certain number of turns has passed since the level began or since the character last used its power, whichever is most recent. Each of the Doctors' powers can only be used after the player has completed a certain number of combos, and has a second-tier stronger effect if additional combos have been completed.
Direct damage
Some characters have powers that deal a fixed amount of direct damage to all enemies. When used, the character with the power deals the specified amount of damage to each enemy, modified by gem color affinities.
Increased damage
Some characters have powers that increase the damage dealt by matching a certain color of gem. When used, each gem of the appropriate color on the board at that time will be marked with a plus symbol. Any combo made that includes one or more of those gems will grant an additional 0.10 multiplier to that combo's attack strength for each of those gems used.
Healing
Some characters have powers that heal the team by a fixed amount.
Color changing
Some characters have powers that change gems of one color into another color. When used, each gem on the board of the first color becomes the second color.
Stun
Some characters have powers that stun an enemy for a certain number of turns. When used, the targeted enemy will be unable to do anything for that duration.
Miscellaneous
Some characters have powers that heal the player's team of poison. One character (UNIT Soldier) has an ability that poisons an enemy for a number of turns. One character (Porridge) has a power that deals an amount of damage to an enemy after a number of turns have passed since it was used.
Enemy powers
In addition to attacking, some enemies also have powers that can be detrimental to the player. Depending on the powers it has, an enemy can stun a character on the player's team for a number of turns, lock a number of gems on the board (prevent them from moving), neutralize a number of gems on the board (prevent them from being part of a combo), change all gems of one color to another color, remove all gems of one color from the board, weaken the pink gems on the board, poison the player's team for a number of turns, deal a delayed amount of damage to the player's team, or heal itself.
Damage formula
The damage formula for a given character's attack versus a given enemy is as follows.
![{\displaystyle {\text{damage}}=a*(1+[N-1]*0.25)*ATK*\sum _{m\in M}[(1+[g-3]*0.25)*(1+p*0.1)]}](https://services.fandom.com/mathoid-facade/v1/media/math/render/svg/5d6361656dc36809d8fcac25a714d2ad657c7565)
Where a is the affinity multiplier (2 if the gem color of the attack is strong against the target, 0.5 if it's weak) and N is the total number of combos made. The summation represents the sum for each combo m over all matching combos M, where g is the number of gems matched in m and p is the number of powered-up gems (from increased damage powers) used in m.
For example, a turn in which two blue combos are made (and no other combos), one with 4 powered-up gems and another with 3 non-powered gems, the summation would yield the result 2.75: the first combo has a multiplier of 1.75 (1.25*1.4), and the second has a multiplier of 1. A blue character would then have an attack strength of approximately 3.44 (2.75*1.25) times its ATK, and the damage dealt to the enemy would be that attack strength modified by the appropriate affinity multiplier.
Some enemies also take less damage from attacks, separate from color affinities, due to damage reduction.
Healing formula
The healing formula is similar to the damage formula, except it uses the team's combined Heal attribute. The formula is as follows.
![{\displaystyle {\text{health gained}}=(1+[N-1]*0.25)*Heal*\sum _{m\in M}[(1+[g-3]*0.25)*\max {(0,1-p*0.2))}]}](https://services.fandom.com/mathoid-facade/v1/media/math/render/svg/ca8d98838be6ce462510a722c16e43ee8e7b7d37)
Where, similar to the other formula, N is the total number of combos made, and the summation represents the sum for each combo m over all matched combos of pink gems M, where g is the number of gems matched in m and p is the number of powered-down gems (from enemy powers) used in m.