For attacks champions use, see Attack
When the game was first introduced with random factor rules, a champion's attack strength determined how likely an attack would be successful. If a champion's defense was much higher than an opponent's attack strength, the attack was more likely to miss.
The random factor setting was removed within a few expansions of the game launching, likely attributed to the fact that it introduced too much randomness into the game. Players could still choose to play with random factor, but Attack instead had a new purpose:
If an attacker's Attack strength was higher than the target's Defense strength, the attack's damage would get a percentage increase equal to the difference. So 20 Attack versus 15 Defense would translate to a 5% damage increase.
If an attacker's Attack strength was less than the target's Defense, the attack's damage, the attack's damage would be decreased equal to twice the difference. So 15 Attack versus 20 Defense would translate toa 10% damage decrease.
This was a decent system theoretically, but it became hard to figure out how much damage any particular champion would do since trying to compute several obscure percentages each turn was infeasible.To simplify the game, the Defense mechanic was changed to be easier to compute. Attack Strength was removed from all Champions, and as a result, champions who had low Attack strength got their damage decreased a little, and champions with high Attack strength got their damage increased. Further, mechanics which affected Attack strength such as Sand Spray were changed to be similar when champions were updated.