Hmm... a Shield Wall sounds like something that would mainly defend other units. Perhaps one or a few of the below:
- All other units in the stack gain +1 stone skins (as per the spell, i.e. ignore one hit) per shield wall in the stack, though only for defensive combat. (Balanced due to the limit of three shield walls per civ.)
- All other units in the stack gain immunity to first strikes, again only for defensive combat.
- Other units sharing a stack with a Shield Wall gain resistance to collateral damage - the Shield Wall, however, is extra vulnerable to it. (They spread out to help protect all the other units.) A shield wall with Magic Resistance could perhaps gain access to a similar stack-defense promotion against magic spells.
- Slap the 'Heavy Fortification' ability I suggested elsewhere on them, doubling their dig-in defense bonus.
Flurries, now, are a bit harder... a defensive collateral damage would make sense, as does a large number of first strikes... I'll put a first strike idea here, instead! Let units with first strikes apply them whenever either side withdraws, as well as at the start of combat - i.e. a flurry with 5 first strikes faces a horseman. Flurry gets five first strike, regular combat takes place, horseman withdraws. Flurry now gains five more first strikes before combat really ends.
Beastmasters, finally... letting them work with captured animals to raise more could work: Say, capture a bear, sacrifice it with a beastmaster spell to build a bear den that keeps producing friendly bears over time. Letting them gain abilities from animals could be interesting, too: Join with a panther for stealth, join with a bear for +2 strength, join with a wolf for a forest movement bonus, an elephant for collateral damage, and so on.
