When you make a match, deals damage equal to the highest damage value in that color. You will see the hero with the attack power will leap to the front--that is the attacking character.
When you make a 4- or 5-match that destroys additional tiles in a row or column, the attacking character will use their values for the destroyed tiles, not the character with the highest.
E.g.: Storm has 65 blue damage and 12 red damage. Her teammate Ares has 65 red damage.
Storm makes a 4-match, destroying a row containing 4 blue tiles and 4 red tiles. She deals 308 damage (12+12+65+65+65+65+12+12). Ares better Red attack is not counted--the match does not do 520.
Subsequent matches in a cascade--including the "second" match when you create two matches simultaneously--will be reduced by 25% each time. You will see the attacking hero (with the highest attack power in that color) will quickly leap to the front on each match, before your first attacking hero returns to the front when the cascade is over.
If your tile swap creates two matches, the first match evaluated is the one matching the color of the tile you moved to make the swap. When a simultaneous match is made during a cascade (or power activation), the board is evaluated row by row, left-to-right, and whichever match contains the topmost, leftmost tile will be dealt first.
You make a match dealing full damage. The tiles fall creating a cascade of 2 more matches. The topmost, leftmost match will do 75% damage and the next (third overall) will do 9/16 (56.25%) damage.
After cascade reduction is applied, strike tiles or enemy protect tiles are applied to the total damage. (That is to say, strike tiles do not get less effective as the cascades continue).
Critical tiles multiply the tile damage times the number of tiles in the match (including the critical tile), times the attacking character's critical value.
In a 4+ match that destroys other tiles, only the tiles that are part of the match are multiplied. Other tiles destroyed in the same row or column will do normal damage.
When multiple critical tiles are in the same match, things get crazy. 2 crit tiles turn a 4.5x modifier into x8; A 3.5x modifier turns into x6. (It's double the modifier minus one.)
This is why 2* Bullseye's expensive black power is well worth the cost. The ability to place 2 tiles next to each other makes it relatively easy to make 8x 5-tile matches, or 3 tile x8 + 3 tile x8 (* 0.75 cascade). Multiply that by an ally 5-star's damage... Or place them adjacent to an existing crit... The numbers get really, really high.