Which abilities contain mutagen slots?
Solution 1:
List of talents containing mutagen slots:
Training tree:
- Arrow redirection
- Fortitude
Swordsmanship tree:
- Invincible
- Combat Acumen
- Whirlwind
Magic tree:
- Enhanced Yrden Sign
- Sense of Magic
- Control over the Power
Alchemy tree:
- Condensation
- Metathesis
- Berserker
- Mutant
- Amplification
You only need one point invested in a talent to mutate it.
Solution 2:
Mutagen: Hit 'C' key to open character screen. Click on 'Training', look at the tiny circle [top right] of the top 2 talents. Right click on talent, select your mutagen and then apply.
Same applies to 'Swordsmanship' talents, although it'll be quite awhile until you reach the end of the tree where the mutagen slots appear.
For 'enhancing' swords and armor that have those tiny slots [top right of item], you'll need to go to a craftsman. I'm not sure if you can remove or replace one enhancement for another, once applied to item.
I have found 'Critical Effect Mutagens' that will help boost your 'Critical Effects' [i.e. bleeding,poison etc.] chance. You can find what % chance you have of activating these Critical Effects within your 'character' ['C'] screen. Now press 'Enter' key to access your attributes, then click on 2nd tab at top right. At the bottom left, you'll see Critical Effects percentages listed. Bear in mind, you must have your sword drawn to have its effects shown on this screen. From there you can use 'Brown Oil' for example in battle via Inventory screen dragging to weapon, or prior to boost that bleeding Critical Effect chance by 30%.
Have fun!