Not sure if this is the correct forum for it, but here goes:

Can heroes ever become upgraded troop types? For example, may a hero mordor uruk ever become a Black Guard? This seems particularly crippling to the mirkwood "spider" models, who will stay at move 8 and fight 3 even if heroes, and seem to be unable to become giant spiders.

Nope, heroes don't upgrade. Instead they level up every 5 xp and increase stats and such. Statistically they can match the stats of an upgraded unit, but they do not upgrade like regular warriors.

Do you think it would be game breaking if, say, on the roll of a 5 or 6 at promotion, after gaining at least 25 xp, you can instead choose to upgrade the hero as if it were a warrior, keeping its other stat upgrades?

There is no point. The heroes can level up farther than upgraded units, and can buy any item available to their race. You can literally build the upgraded unit

By the time the hero gets 25 exp, the chances are that it will already be better than his unit promotion counterpart.

jadin27,

Good question! Others have stated that it is pointless because heroes can become better than the upgrade. This is not entirely true, because if you (in a world where your question becomes true) have a Rohan Warrior hero promote to a Helminga hero then you'd have a sudden strength upgrade.

While working on the project, I believe we opted not to have this upgrading path for two reasons:

1) It gets a little muddy when it comes to the simplicity that Baker strove for.
2) Your hero is now on his own path, separate from his similar warrior friends. This path will change him entirely as a person and in his identity.

However! If your hero is a Warrior of Rohan model and you upgrade him a lot, there is nothing stopping you from using a Rohan Royal Guard model to represent your hero. He is a hero and can be represented as bland or fantastic as you want, following WYSIWYG.

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- Wild
Battle Companies Developer

(CE) Battle Companies 2016 Edition