This is a good thread. I'm the first one to complete a mod based on its ideas. Ha!
It has four seasonal spirits and one improved Mechanical Man commander. I've tested the units and they should work fine, and the spells appear, but I haven't tested if they summon the correct creature (or anything at all).
The mechanical giant is non-unique, has full slots, full immunities and enc 0, but 40 hp and mr 12. It might still be too good for its price (15 gems). The seasonal spirits are also non-unique, and might also be too good for
their price: 150 gems. Yeah!
Primal Hunter: Water 4 Air 3, paralyzing melee attack, armor-piercing bite, chill 19 and host of winter wolves. Stealthy, fast, sailing.
Thunderbird: Ethereal Great Eagle with undead secondshape, Air 4 Death 3 and armor-negating AoE lightning attack. Flying, even better mapmove.
Golden Lion: Ethereal lion with huge poison aura and fire shield 10 and bite with Deadliest Poison.
Great Bear: Green, ethereal bear with even more hp than the others, N4 E3, trample and regeneration, good prot, huge strength, heals its own afflictions. I'll give it reinvigoration if it's too weak.
All summon fitting beings: summer lions/green lions, spring hawks and great eagles, fall bears and earth elementals. Primal Hunter summons only Winter Wolves, but it gets 5 of them every turn. All cast Living XXX in the beginning of every battle.