Gem Usage in Battle

[Chazar]

What are the criteria for gem usage during battle?

I just lost a fully equipped Rudra (and probably the MP game) against Vanheim 25PD. The Rudra was scripted to cast SoulVortex, Bless, PhoenixPyre, Bless, HoldTurn&Attack. Instead of using one of the 5 death gems in his pocket, he just went straight to around 50 fatigue by casting SoulVortex without a gem. Being highly fatigued, despite E4 bless and BootsOfTheMessenger, he did not use one of the 3 fire gems for PhoenixPower. Since the first self bless had actually hit him ok, instead of the second bless spell he choose to case some insignificant death attack spell without a gem, bringing him above 90 fatigue, which of course resulted in certain death.

I remember Dom2 mages being very eager to use up all their gems before casting spells that actually require gems, so I thought 5 death gems would encourage the Rudra enough to use one or two to lower the fatigue from SoulVortex, but apparently a 40 fatigue spell + encumbrance from HydraSkin is not enough to warrant gem usage in Dom3.

• Does battle gem usage depend on how fatigued the caster already is? (i.e. would the Rudra have used its death gems if I had first scripted PhoenixPyre, Bless and then SoulVortex)
• Is there a known threshold for using gems to avoid fatigue, besides 100+ fatigue spells?
• Does the number of gems in the mages pocket influence the likelihood of gem usage to reduce fatigue?

I would like to generally understand how the AI decides upon gem usage, the Rudra example is just an example from an ongoing game, which should otherwise not be of interest here.

[Samhain]

According to the unofficial Dom3 Wiki, gems are only used to reduce spell fatigue to 50 or the lowest amount possible above 50.

See: http://dom3.servegame.com/wiki/Gem_use

So, your Rudra must have been right on the cusp. Perhaps he would have used a gem had he more than 10 points of spell casting encumbrance.

To avoid the issue with an undesirable spell being substituted for a redundant bless, I would set the Rudra off in a corner by himself to ensure that the bless falls on him. That way, you can either put something you really want him to cast in the slot that had the second bless or script him to attack one battle turn sooner.

[thejeff]

I would assume the "Is this battle a big enough threat to use gems" calculation, applies to using gems to counter fatigue. I'm not 100% sure, but it looks like that is what happened. 25 PD wasn't enough of a threat, so the fatigue checks didn't even come into play.

As a side not, if your Rudra is going into battle alone and the enemy has no fliers, it should be safe to only cast bless once. Self-bless will always hit if he is the only target within range, which if it's early in the script means fliers.

[Deathblob]

If you view the battle with -dd on, then you can see if can_use_gems is 1 or 0. If it's 0, then he won't ever use gems in the battle, unless you hit the bug where he starts using gems when the enemy routs.

If it's 1, then you are better off saving the higher fatigue spells for later in the script, since if current fatigue is 0, the caster will be unlikely to use gems for fatigue reduction even if the spell has a fatigue cost of 80 or something.

If you're casting Soul Vortex, you might want to bring friendly battery units along with your Rudra to leech health off of. Make sure you don't hit the auto-rout HP limit though.

[thejeff]

Battery units are tricky to bring if your Rudra is cloud trapezing, which is usually the case.


Also remember, if you're cloud trapezing to attack and you do take the province, your enemy might be moving troops into the province. If he is, they'll arrive after the first battle and fight a separate one. If you're out of gems now, you're also in trouble.
Relying on gems to keep a raider's fatigue down or to get buffs off at all is risky. Not to mention a pain to keep him supplied with gems. Even with the gem use you'd be high on fatigue those first couple rounds of combat. A couple of lucky hits and you can be in trouble.
Going with weaker but cheaper buffs might be better.

[brxbrx]

Is this for vanilla?
Man gems sound confusing.

[Finalgenesis]

The gem mechanic is fairly simple, the AI mechanic (which I assume you're referring to) and trigger conditions for gems however is a total nightmare.

You get use to it, but you can manipulate AI only up to a point, the other 50% is crap-shoot, not a totally bad thing though, if immensely frustrating.

[Deathblob]

Originally Posted by thejeff

Battery units are tricky to bring if your Rudra is cloud trapezing, which is usually the case.

A few blood slaves would work.

[Chazar]

Thanks for the many useful answers!

If I had only known those a single turn earlier! I guess that either knowing about the corner-self bless and/or the blood slave batteries would have saved my day. I did already account for a battle in the normal turn phase, which is why the Rudra had 5 or 6 death gems - which I thought would be enough to cast SoulVortex twice, but according to the above link Wiki page, he would never use those anyway with that script. Good to know that the Dom3 is not so wasteful on gems.

[LDiCesare]

Originally Posted by Samhain

According to the unofficial Dom3 Wiki, gems are only used to reduce spell fatigue to 50 or the lowest amount possible above 50.

Which may be right but the ai will spend much more than that.
I had a S9 oracle scripted to cast magic duel*4+returning. It needed 11 gems to do so despite the ridiculously low cost of magic duel for an S9 mage (100 fatigue but 8 levels over the required level).