Auric eeds to be immortal unless killed by the godslayer. Normal units can still have their chance at "killing" him, but it would only earn them temporary respite, and far less experience than properly killing him, if any.
I've also mentioned before, some of his other flaws
1. He needs a lesser proportion of ice strength. As is, he's too vulnerable to magic immune units.
2. Snowfall should destroy roads, to prevent sneak attacks on him from afar.
3. He needs the cannibalize promotion, or something similar, so lots of little units can't be used to weaken him..
4. He needs blitz. Come on, really. A god who can only kill one thing per turn is pathetic.
Again I agree with almost everything except for blitz and maybe cannibalize. Blitz because I feel that it should be the job of snowfall to actually kill massive stacks of enemy units and cannibalism only because if you make him immortal then having him fall to massive numbers won’t be an issue.
I also suggest a massive overhaul of how his abilities work. You see, Mulcan is supposed to be god, meaning that he would be able to affect the whole world and not just the place where he is currently standing. His power should be felt no matter how far away they are.
I think he should be given a spell that functions like the ICBM from vanilla civ, dealing massive damage to any unit in a 3x3 area, destroying all improvements, lowering city population and turning the surrounding tiles into ice (changed from deserts/fallout). However, instead of causing global warming it would cause global cooling. Having it used a lot during the game would cause random tiles to change into ice rather quickly. Using it would also reveal the position of Auric on the global map.
I think this is balanced by the fact FFH spell system only allows a unit to cast a single spell every turn making abuse of this impossible. However, there remains the issue of flight and high speed, so obviously it should not be usable in terrain where he could not normally walk and once used it would make Auric lose flight for the rest of the turn and have only a fraction of his speed on the next. Auric himself and the unit wielding the Godslayer would be immune to this ability while units with spell resistance would only have a slight defense (Avatar does lower spell resistance by -50%).
This will make you truly feel like you are controlling a god rather than just a strong unit.
Another idea that was suggested (not only be me) is to have Auric turn water into ice allowing Illian armies to walk across oceans on a trail of ice would further enhance the role of intercontinental warfare that Auric currently holds.
Another idea that was suggested was to have the Illians auto win once they have Auric Ascended and a certain % of the world is covered in ice. While I think that this is nice it just doesn’t give the same sense of satisfaction. I suggested that once a large part of the world is covered in snow (probably around 75-80% of the landmass) Auric could use something akin to an Ultimate Stasis, working the same way as the world spell but having an infinite duration. Granted this is basically the same as just winning the game but on the other hand it would truly allow the player to feel what it is truly like to put the world into eternal stasis as the God of Winter. The only way to end this would be, of course, to kill Auric with the Godsalyer as Kylorin had done in his time.
Lastly there just remains the issue of improving Auric’s death animation and the effects of his death. But these problems are really a no brainer and are easily solved without input from the community. It is only important to know that they are there, the rest I believe, will sort it out eventually.