Slitherine

Looks pretty much random when they appear?
Just wondering if it can be predicted in some way, like one every 100 xp or so. Haven't really paid much attention to it.

Heroes can be awarded when a unit has a certain number of kills, but it is partially random. For the normal campaigns, the first hero can appear when a unit has made at least 50 kills, and it will almost certainly appear when you go over 100 kills. So normally, a unit will get its first hero when it has between 50-100 kills. The second hero can be awarded when a unit has between 101-300 kills, and the third is possible between 301-500.

So if a unit doesn't have a hero yet but is close to 100 kills, you can expect one soon. I've managed to save/load in such situations to 'discourage' ( ) the '+1 movement for your fighter' types.

Kills needed to get a hero in the Grand Campaign:

1st hero: 100-300
2nd hero: 301-1000
3rd hero: 1001-2000