Leather is a common material among the Hellhorned, so I've lined my garb with the material for protection. Given the stench, I'm sure the source of it is better left a mystery.
Fortify is a fairly low-impact, low-risk, easy-to-use card that provides a little bit of extra defense for a unit. In most combats, it should simply be applied to a front line unit that needs to be able to take more hits.
One particular strength of Fortify is its ability to easily strengthen frail back-line units in situations where they may otherwise be in danger, whether due to Sweep or Spikes. (That being said, this card often doesn't provide enough defense to warrant taking Retribution as a Trial if you are relying on frail back-line units to stay alive to win.) Hornbreaker Prince (especially its Reaper line), Horned Warrior, and Branded Warrior are examples of units that appreciate this.
Generally, decks that want to draft this card are ones that appreciate this strength, or simply have a lot of card draw.
None. None of the common upgrades can be applied to this card, and the rare upgrades generally do not have enough impact to justify their cost.
See: Version History