Complex sentence: A major feature was the influence of Chaos forces through unsealed portals, which the player would have to close; while in areas affected by Chaos, the player's character would become tainted, causing mutations that may be either detrimental or beneficial.
Split into simpler sentences: A major feature was the influence of Chaos forces through unsealed portals, which the player would have to close. While in areas affected by Chaos, the player's character would become tainted, causing mutations that could be either detrimental or beneficial.