Lefsi Spiritchaser must stay alive or this quest fails.
He does not move and is a Ritualist with a few skills to keep himself alive if one or two enemies go to him for a short duration.
To trigger the first wave you must speak to him (they will spawn right away).
There is a total of 6 waves that spawn one after another once every enemy of the previous one is killed.
Can check the wiki page to see the chart, builds, and other information: https://wiki.guildwars.com/wiki/A_Good_Deed.
Wave Southwest West Northwest
1 Necromancer Shadow Vaettir x 1 Necromancer Shadow Vaettir x 1 Necromancer Shadow Vaettir x 1
2 Mesmer Mist Vaettir × 2 Necromancer Shadow Vaettir x 1 Mesmer Mist Vaettir × 2
3 Monk Smite Crawler × 2 Warrior Grasping Night x 1 Monk Smite Crawler × 2
4 Monk Smite Crawler × 2 Monk Smite Crawler × 2 Monk Smite Crawler × 2
Elementalist Stalking Night x 1 Elementalist Stalking Night x 1
5 Warrior Stalking Night x 1 Warrior Stalking Night x 1 Warrior Stalking Night x 1
Elementalist Stalking Night × 2 Elementalist Coldfire Night x 1 Elementalist Stalking Night × 2
Elementalist Stalking Night × 2
6 Mesmer Tortured Spirit × 3 Mesmer Tortured Spirit × 2 Mesmer Tortured Spirit × 3
Mist Vaettir and Tortured Spirit have IW so be careful in melee range. Stalking Nights both Warrior and Ele are not a problem as all they do is auto attack and KD. Grasping Night is similar but it can rupt. Coldfire is the usual Ele and the Shadow Vaettirs have Unholy Feast. Smite Crawlers of course have a lot of close damage and Shield of Judgement.
Tactic: Stand in the middle spawn and aggro everything using a bow or low HP/Armor set as necessary to make sure all of the aggro comes to you, and kill the groups on you.