I've done a fix which should work, I'll push it before too long.

If d = 0, d_test < 0 when choice[i] = -1

Perhaps including this:

If (d_test < 0) d_test = 7;

*facepalm*

Fix pushed, I went with which I think kills the problem dead.

Nice! Learned something new...

Ive uploaded all these changes to the playstore. The blackguard is a nice opportunity for me to rethink the spell ui in Android.

Response has been good so far, and the feedback is helpful. I'm going to post an outline here to hopefully generate further discussion.

1. Impaired Recovery
   1. Impaired HP recovery (1/2 speed)
   2. SP degen (1/2 the rate of normal SP recovery)
   3. IMP_HP and IMP_SP have no further effect
2. Ways BGs gain SP
   1. Gain 5% of max SP for a full round of melee attacks
   2. Attacked for X% of max HP, gain X% of max SP
   3. !Restore Mana or other items
   4. Hurting self not allowed
3. Casting and SP Degen heal HP
   1. Spending X% of SP heals X/2% of damage (max 25%; spending >50% of mSP in one spell is inefficient)
   2. SP degen is 2x more efficient at healing, but obviously slower
   3. SP gains above max SP are wasted
   4. Resting and Regeneration flag double SP degen *only if* the player is hurt
4. Max SP taken to be at least 10 for SP gain and healing.
5. Spell list (not going to itemize every spell here)
   1. New melee spells
      1. Leap, Whirl, Maim
      2. Every 5 levels one of these becomes available or increases 1 blow
      3. Number of blows does not increase with lighter weapons, higher strength, +blows gear, or other effects
   2. Short effect lengths
      1. Berserk Strength starts pretty short, but gets longer (8+1d8 to 55+1d55)
      2. Grim Purpose 12+d12, Taunt 10+d10, Venom 20+d20
      3. Bloodlust 10 (extendable)
   3. Only half-caster to have a shapechange (Werewolf Form)
6. Skills (initial +bonus every level)
   1. Shoot skill down to 35 +1.5, worse than all except Mage and Necro
   2. Throw 40 +3, equal to Druid
   3. Hitdie 8 (Warrior 9, Rogue and Paly 6)
   4. -1 -0.1 stealth - never before seen in Vanilla (I think?)
   5. 60 LB armor limit for casting - 50% more than any other casting class
7. Global changes
   1. =Open Wounds sometimes available in Magic Shop (546 AU)
   2. Berserk Strength (SHERO) applies only to melee, and stops natural HP recovery

Confused by a couple of things. Current weapon says it does 2.7 blows per round. It's an artifact dagger, lightweight. If I cast Whirl for example, it says it does 2 blows per foe. I'd then expect it to deal 5.4 blows per foe but that is contradicted by your last point. At some point there is a tradeoff where the weapon's solo # of blows is better or worse than the spell. I had been using the Whirl spell regularly when next to 2 or 3 monsters but will have to reconsider.

I also expected the Whirl spell to generate extra SP because you are hitting multiple foes, but it doesn't seem to work that way.

And at the moment the Maim spell only does 2 blows plus a stun. Not that useful yet.

The stun effect of Maim is nice. But at high levels (not there yet) you get 3 blows max. How about making each blow unavoidable? Less blows, but each one of them lands on target. Or reduce the evasion chance

Blackguard Shape-Change?
 

"Only half-caster to have a shapechange"

What's the change? Are we envisioning a Cuchulainn battle-fury type effect or an animal/creature label?

"The first warp-spasm seized Cúchulainn, and made him into a monstrous thing, hideous and shapeless, unheard of. His shanks and his joints, every knuckle and angle and organ from head to foot, shook like a tree in the flood or a reed in the stream. His body made a furious twist inside his skin, so that his feet and shins switched to the rear and his heels and calves switched to the front... On his head the temple-sinews stretched to the nape of his neck, each mighty, immense, measureless knob as big as the head of a month-old child... he sucked one eye so deep into his head that a wild crane couldn't probe it onto his cheek out of the depths of his skull; the other eye fell out along his cheek. His mouth weirdly distorted: his cheek peeled back from his jaws until the gullet appeared, his lungs and his liver flapped in his mouth and throat, his lower jaw struck the upper a lion-killing blow, and fiery flakes large as a ram's fleece reached his mouth from his throat... The hair of his head twisted like the tangle of a red thornbush stuck in a gap; if a royal apple tree with all its kingly fruit were shaken above him, scarce an apple would reach the ground but each would be spiked on a bristle of his hair as it stood up on his scalp with rage."
— Thomas Kinsella (translator), The Táin, Oxford University Press, 1969, pp. 150–153

Right. It's not "2 rounds of blows" per foe. One of the goals, right or wrong, was to reward Blackguards for using big, heavy weapons. Whirlwind Attack in particular is easy to see why this might be the case. You have to spin the weapon and maybe your whole body 360 degrees for each blow. Using a light weapon such as a dagger wouldn't make it much easier to do that.

Yes, totally. Not sure if this is good or bad, but I personally think it's fun and interesting. For example, at CL20 Leap grants 2.0 blows. There's a really good chance that your character has 1.3 blows or less at that point. So it becomes a nice spell to cast even adjacent to an enemy, if you have the SP to spare. There's a lot of these little boosts and inflection points along the Blackguard journey. (By inflection point I mean a place where the optimal strategy changes.)

Yeah, I thought about that but it doesn't seem to make much sense to give SP back for spending SP. I'd rather focus on giving you good value for the SP you do spend.

It might surprise you how effective stun is. I have written down: "Damage reduced 25%. Accuracy reduced 25%. 10% chance to miss a turn. Gives player +10 to-hit for crit calc only. See mon-timed.h and test_hit in player-attack.c." It might do other things, too. But at a minimum it's very effective at reducing the damage you take in melee combat.

Thanks so much for the comments and questions!! As I've said a few times, this is not a complete work, and the feedback is very influential. (Might not be significant changes before 4.2.1 release, depending on Nick, but I do have changes planned over the next few months.)