Casting source magic requires source points. This video will guide you through the whole process of getting souce points and the three source magic skills (b. Chapter 4 - Mastering the Source, quest walkthrough and hints. This meta quest will automatically be added to your journal upon arrival at the Reaper's Coast. This quest describes your overall progress in the fourth chapter of the game.
Source Powers
Apart from scattered Source pools, there's the Source fountain Stabbey mentioned behind a door in the ruins where you rescue Gareth, which you'll also find in the Hollow Marshes. Click the fountain to create a Source pool and have your collar-less characters walk over the pool to absorb it. Repeat until everyone's full-up on Source! Using the skill will use up the source power. How to acquire source point: In Divinity Original Sin 2, there are some areas covered with source water, let your characters stand on them and you will gain source points. For example, in first chapter, there is a pool of source water in The Hollow Marshes and another in Necromancer's Tower.
Your characters whether they are custom made or origin stories all are sourcerers which means that they all have access to the Source. The Source is essentially the energy behind the creation of life in Rivellon and as you can imagine gives access to great powers to whoever has access to it. In terms of gameplay the Source is not only connected to the previously mentionned effects Bless and Curse as you need access to the Source to use those but also gives access to special skills much stronger than the others. Those Source skills cost you a Source point to use on top of the normal conditions such as Action point cost and cooldown. Source points can be acquired by different means such as walking in a Source pool that you can find regularly around the world, by draining the Source out of corpses or by draining the spirit of the deads thanks to your Sourcerer ability to talk with spirits. But beware as draining the Source from the deads may lead you to become dark and have terrible consequences …
As you can imagine using the Source is not something you do often and should be done only in the toughest encounters or you may regret being out of Source points during the most dire situations. You start up with one maximum Source point per character as soon as you remove your Source collar during the Prologue on Fort Joy’s island and then as you become stronger may eventually get access to up to 3 Source points stored at the same time.
As a general advice aside from not randomly using Source skills I would recommend you to specifically wait the right window to do so. Always use your Source skills when you know the correct armors are removed on your targets (or that your skill will remove them in the process as most of those skills are very powerful) to maximize its effects. Or wait to be able to target as many enemies as possible if you use a big skill that can impact several targets.
Here is a comparison from the same character of a Fireball regular skill and Epidemic of Fire, a source skill. At first they look not so different in terms of damage but Epidemic of Fire can bounce up to 5 times and also leave a cursed fire field instead of regular fire making it a very deadly weapon melting down your opponents.
It may sound a bit trivial but try to use only Source skills that really take the best advantage of your strengths and strategy, don’t use a Source skill just because you can use one. For example if your have a mage with particularly good fire damage and very average access to other elements try to mostly (if not only) make use of his fire Source spells because those bonus damage can really quickly ramp up and decimate your foes.
Divinity Original Sin 2 Level Cap
Though at first Source skills may look a bit underwhelming considering their cost if you use them at the appropriate time and have a build that make good use of it they can be really devastating and turn the tides of battle in your favor with one Source skill only.
Divinity 2 Max Source Points
The walk-through at https://steamcommunity.com/sharedfiles/filedetails/?id=1139237003 does the Roost/Saheila quest for the 3rd point, but defers it until lvl 15. Is there any reason not to do it at lvl 13, right after Mordus? Enemies are only lvl 14 and my optimized party is tearing through content, so difficulty shouldn’t be an issue.