1. Heart of Stone should be Heart of Earth. Sorry; got mixed up with my "dirt" synonyms.
2. Sad that I picked 3 duplicate spells; I'll fix that.
3. Unarmed Strike might be a good idea; I'll fix that.
4. I like your suggestion for the Noble Phantasm
How about the following for Sadlygrove/Rubilax?
Heroic Spirit Include: Sadlygrove summons forth a terrible demonic Greatsword named Rubilax. It gains Maiming (MiC) at 7th level, Crazed (AEG) at 11th level, and Clouting (CArc) at 16th level.
Shushu's Strength (Ex): Sadlygrove is terribly, horribly strong. As a standard action, the servant soul may make a single melee attack; if the melee attack hits, it automatically threatens and confirms a critical. This deducts 2 rounds from the Install's duration.
Heroic Spirit Install: The servant soul's skin turns a dark grey color, and muscles bulk to grotesque extremes; Rubilax screams curses and violence before vanishing, and a blood-mad demon eye opens in the middle of her forehead. She gains bonuses to Fortitude Saves, Strength, and Constitution. She grows a size category; replace the normal bonuses and penalties to ability scores with +2 Strength and -2 Dexterity. In addition, she triples the distance of any jump she makes, and may treat her Unarmed Strikes as two-handed weapons for all intents and purposes. Finally, she gains Improved Unarmed Strike and Superior Unarmed Strike as bonus feats; her Unarmed Strike automatically gains the same special abilities and enhancement bonus as Rubilax, and also ignores Hardness.
If the servant soul's bonus to Strength from this Include equals or exceeds 12, she gains an additional size category, replacing the normal bonuses and penalties to ability scores with +2 Constitution and -2 Dexterity; in addition, she ignores any resistance or immunity to critical hits that a creature at least two size categories smaller than her may have, and increases the critical multiplier for her Unarmed Strikes to x3.
As long as Sadlygrove is Installed, the servant soul cannot wield any weapons, is subject to all the penalties and restrictions of a Barbarian's Rage, and considers her alignment to be Chaotic Evil.
Rubilax's Indefinite Growth (Ex): Rubilax is a Four-Element Shushu, a dark spirit of Strength and Destruction; his strength is terrible and nearly limitless. As a Swift action, the servant soul may tap that well of Strength; each melee or ranged attack they are struck by before the end of the round increases their bonus to Strength from the Install by 2 for the rest of the Install, to a maximum bonus equal to their class level. In addition, the servant soul regains 5 HP each time she is struck by a melee or ranged attack that round. This deducts 1 round from the Install.
Berserker Sir Sadlygrove Percedal's Spells: 1 - Vision of GlorySpC, 2 - ZealSpC, 3 - Dolorous BlowSpC, 4 - Heart of EarthCM, 5 - Irresistible ForceGh
Quick summary of changes:
1. Boosted the character's FISTS; namely, I replaced the Rock Hurling feats and Slam attack with Improved Unarmed Strike, Superior Unarmed Strike, and the ability to use their unarmed strike as a two-handed weapon.
2. Boosted the Noble Phantasm; you now gain a +2 bonus for each attack, and regain 5 HP any time someone hits you.
3. Boosted the size increase a little; now you can ignore any immunity to critical hits that puny creatures might have, and your Unarmed Strikes have a critical multiplier of x3. Which synergizes well with...
4. The revised Shushu's Strength; now it allows you to auto-crit. Still as a standard action, since I never really saw Sadlygrove as a charge-booster; I mean, you can use him for that, but his big size/strength increase precludes wielding weapons, and his Phantasm can't be used on a charge.
5. I... can't think of any good 1st or 2nd level spells that you haven't already taken. And I had to go kinda obscure for the 3rd and 5th level spells. Dolorous Blow doubles Crit Threat range and auto-confirms criticals; Irresistible Force is basically Freedom of Movement + UNSTOPPABLE FORCE, FOOLS. Do you have any suggestions?
In all, Sadlygrove should be a bit more synergistic.
EDIT: I figured out spells for 1st and 2nd level! Huzzah!
Oh, and that makes sense for the Devoted Soul/Initiate Soul.
A different question; if your game is otherwise using Homebrew disciplines, can you choose to replace the disciplines associated to your different Heroic Spirits?
For example, gaining God Slash maneuvers for your Saber, or Infernal Monster maneuvers for your Berserker. Or just replacing White Raven with Scarlet Bravura.