When you have online connectivity enabled, you’ll be able to see the spirits of units who perished in other players’ battlefields. This helpful feature will help you identify which are the “hotspots” or dangerous areas where most units fell most often. A good example will be this area around the Death Knight, in a story mission early in the game.
Yellow spirits indicate a space where many allied units were defeated. Stepping on this tile will give the unit bonus experience or restoration of the unit’s Weapon Durability.
Purple spirits indicate where many enemy units have fallen. Have an allied unit end his/her turn on top of that tile where the spirit is to get some items.