When you play any game and you win, you want it to be because of your own decisions you made and not because the opponent let you win. The vanilla XCOM2 AI lets the player win by often intentionally doing a suboptimal thing. This was removed. The Better AI plays to win. This increases the game’s difficulty, but also the satisfaction you can take out of winning your battles.
Depending on the difficulty, vanilla XCOM applies a limiter to the number of engaged enemies. Enemies over this number would take only defensive actions and not actively fight back. Only on Legendary, this shackle did not exist. A Better ADVENT removes it for all difficulties.
Removed: Spread fire
When deciding on where to shoot, vanilla XCOM’s targeting actively prefers to spread fire around. This is meant to reduce player stress by causing more wounds and fewer deaths. This behavior is especially pronounced on lower difficulties. A Better ADVENT removes this kind of handholding completely. In fact, enemies will now start focusing their fire on already wounded soldiers, trying to score a kill.
Reduced: Linger penalty
When deciding where to move, the AI decides how “valuable” every tile in range is, then uses the best. To promote alien movement and prevent shootouts, the default AI penalizes the current tile it stands on by 25%. This large penalty all but ensures that aliens run around a lot, right into worse cover than before and through player overwatches and supression. The penalty has been reduced considerably from 25% to 10%. This still gives a nudge towards movement so that fights don’t stall out completely. But it no longer promotes movement that doesn’t have a specific goal in mind (better shots, better cover…), and units stay in good spots if they have one. This is important to enable longer shootouts between XCOM and aliens.