Pathfinding in games must appeal to player expectations for (i)___________and naturalness, that is, what natural intelligence might conceivably do.

In this sentence you see that the answer should go along with naturalness, and natural intelligence signifies that the correct answer should be in harmony with characters of intelleigence, the only word that fulfills this is plausibility.

Thus, navigation in games is not necessarily (ii)___________for maximum machine efficiency or for shortest distance. Indeed, these goals are assumed to be secondary and possibly even undesirable.


From this sentence we see learn that navigation in the game should be something that is not really done for just reaching the places of action or battlefields (an example of inference from his mention of shortest distance) or to reach machine max efficiency.

permeable doesnt work at all over here so eliminate, and quixotic (unrealistic and impractical) is not what we are searching for. Thus the only positive word left is optimal.

That is, if they lead to unrealistic, mechanical-looking movement that is lacking in sensori-emotional or aesthetic qualities, movement as such (iii)___________players and detracts from the game’s replay appeal and immersive quality.

So if navigation was neglected then the game will lose its aesthetic qualities and it's going to disturb players, asserted by " detracts from the game etc.."

so discomfits is the perfect choice here as embolden and abets both mean to encourage the former is in a positive sense the later in a negative sense.