Do you use the spell Steal Spirit? What is your strategy?

Only when playing Empire, killing people for their magic powers sounds like a thing they would do. On Kingdoms i prefer to make the all Commanders so they can produce money to pay for their own army.

I haven't used it yet and myself questioned how to use the spell best (but without any moral regrets). The late champions are of little or no use to me - and the spell should be useful.

But even though I make my Sov a mage with two schools from start - it's only late, approx level 15+, that she has all talents I want and could use a new spell-line from Steal Spirit. I tried the spell on Bard henchmen but only get the henchmen-line (which only has one ability per magic school), but if the Henchman had Fire 2 then my Sov would get Henchmen-Fire-2. When trying out Steal Spirit on a Hero with proper Fire 2, my Sov would only get Fire 1. (This is all working as intended I think.)

Mage Sov

One option for getting use of Steal Spirit /when playing a mage/ is to skip one magic school when creating your own Sov. Those two points (out of six) instead goes to Talents (e.g. Brilliant, Might) or to Equipment (e.g. Procipinee's Crown, Ereog's Token) and when your 2nd to 4th Hero arrives your Sov sacrifices him to get the wanted school. The plus side is 2 more starting points, the drawback is your mage Sov has to wait with one Magic School, mening no use at all from it at the initial important gameplay. Also the first Champ is needed for a secondary army, as well as the second Champion if I'm playing on a big map and using Beastmaster (taming beasts to send back to Champions armies).  It's a painful delay of magic IMHO and I'm still debating wether I should try it or not.

Might Sov

As a might Sov, I don't think the first spells from Fire1/Water1/etc1 are terribly useful in combat. Your Sov will mostly do more damage by attacking. The single exception I can think of is Death 1 (if Empire), giving you Curse (=foe get defense lowered to 0) and a possible huge bonus vs some hard monsters. If you are prepared to place some more points in the magic, you could consider:

- 1 or 2 additional point to get to Fire 2 for Flame Dart. If you have problem reaching your foe in the first round, this gives you a good ranged spell (2 x level +2/Fire shard damage).  For 2 points you get the options Feedback (=interupt plus damage) and Focus (+25% damage) to cast the first combat round. 

- 1 or 2 additional points to Life 2/3 for Heal and Shrink/Growth. Both of which I think could benefit a Warrior in certain situations.

- 2 additional points to Water 3 to get Spell Leech (and Mantle of Oceans for other casters). This would give you an interupt (same as Fire 3), something you don't have as a might Sov. 

You will have to decide if it's worth skipping a few points from your usual talents (and the moral aspect), for the above.

Yes, I have used Steal Spirit sometimes. I would never build a strategy around it though. That would require save/loading, and I try to avoid that.

Most spell schools do have useful spells at level 1, mostly city enchantments, but also Slow, Haste, etc., so Stealing a School never hurts. Well, it might hurt that champion... so only use it if you know you are never going to use the champion otherwise.

Also note that you can sometimes steal unique spells/abilities from a champion. Worth a try, if you don't have any moral objections.

Yes, there are moral objections. It would be brilliant if I could steal spirit from a monster which I capture.

IMHO a Warrior won't cast slow or haste often, but it's better than nothing (if you cannot get within reach). IMHO you don't gain much from stealing a Magic school 1 unless you want to progress it further up. You loose a Champ who could cast the 1st lvl city buffs spell instead and also sit in a city to reduce unrest or do other unimportant things. (And if I remember correctly Champions don't have salaries.)

And I also noticed, as you write, that stealing from a mage Champion from the mod Champion Bonanza, can give you other spell talents (that you don't want to prioritize, but is nice to have on Sov). These "other spell talents" can be deeper into the mage talent tree (i.e. not magic schools), e.g. some new spells that come from mage talents.

You do not remember correctly, they cost 1 gildar upkeep. The quest/event ones are free, though. Maybe you were thinking of those.

Anyway, 1 gildar isn't much, but neither is 5% unrest reduction. It's up to personal preference.

Thanks, I had one Champion from a quest and must have checked him. Good to know the difference.

Yes I use Steal Spirit.  I don't use it every game, but here are some times that I use it:

1.  Hero has so many injuries that he's basically useless.

2.  Hero that I have no intention of leveling up because he is weak, but he has a nice magic class that would go well with my sovereign

3.  Just picked up my third mage hero (so I don't need anymore) who has something like an Earth III magic class and my sovereign is only Earth II magic. 

Can't you just buy the tomes from Pariden instead of killing one of your units for a spellbook?  I don't see the point

1. Pariden is not in every game.

2.  Buying a book from Pariden won't advance you from Earth II to Earth III but Steal Spirit can.

pretty situational...   Earth II to Earth III is one level up..   I'd rather that than whacking some guy to save 1 gildar a season.   My guys that are worthless I find something for them to do.   Usually hangout in my territory as defense against invading wandering monster.

Pretty situational? Yes!

Kudos to the devs for designing something that's neither useless nor OP 

I rarely use Steal Spirit now I use the Monuments mod - champs can actually level up to decent levels once you have a few of the XP buildings up. And if nothing else, you can level up L1 units as Commanders for the passive bonuses that are a lot more powerful when you don't have to risk combat to get them.

It's a lot easier to get some random champion to go from Level 5 to Level 6 than it is to get my Sovereign from Level 15 to Level 16. Thus, if I want to have an extra level in some random magic school and I happen to have a champion with at least one more level in that magic school than my sovereign has, or who can relatively easily get that one extra level to make it that way, it isn't actually that bad of an idea to off the champion. I only need so many champions to lead my armies, and I only need so many champions to reduce unrest in problem/focus cities. Any beyond that are just extra icing. That being said, I would generally rather off a Henchman or Sion that I gave a spellbook to and then leveled to the appropriate magic skill than off a champion.

Finally I think this spell is the heritage of the original game FE, where there were hordes of heroes, thus sovereign could buff his magic knowledge quickly. Especially if a sovereign is combat oriented he has little time to learn magic. And when come the time for magic, it appears, that new exp level will not be soon, so here comes this spell...