There are numerous ways to deal with felines peacefully, including but not limited to: teleporting them away, pacifying, morphing, luring them into pre-generated traps, and pitting them against other enemies. That's more than enough to make the cat lord quest manageable. However, oftentimes when a player makes a conscious decision to fulfill the quest, they could still kill a feline before they even realized it. For example, by hitting a feline while in the dark, or killing an out-of-sight feline by a bolt bounce or an explosion area. Those things happen.

Since, as I understand, right now the cat lord's disposition towards the player depends entirely on the kill list entries, there is no way to fulfill this quest if you accidentally kill a feline that way. I don't think this is fair to a player who genuinely tries to do everything right. So, my suggestion is to change the disposition—basically, presume innocence on the part of the player based on the following criteria. It would require adding a "seen by player" flag to each generated feline, which would permanently flip to "1" whenever said feline enters the player's line of sight (i.e., when they see the "f").

1. If a feline has never entered the player's line of sight, its death—no matter the cause—should not void the quest;
2. if a feline has entered the line of sight at least once and is hostile towards the player, its death should void the quest but not aggravate the cat lord if it happens under the following conditions:
— the feline is in the dark;
— the feline is invisible;
— the feline is hit by a bolt bounce or an area effect at the moment when the player couldn't see the feline;
— the player is blind;
— the player staggers (such as from being stunned or confused).
Non-hostile felines should be displaced rather than hit.

In my opinion, this will not make the quest easier and will not give the player the ability to abuse it. Still, it'll provide them with certain deserved control over it. I also made it so that it was possible to void t
If a player has killed cats without voiding the quest, or forfeited the quest without aggravating the cat lord, they should receive less points for it, the character summary line about the quest should read differently and dialogue with the cat lord himself should have some differences.