I'm a bit confused about how Realms work. I also understand that the realm rules often have local variants on how they are used, so for this discussion I'm just trying to understand them as presented in the core rules and the General's handbook. As I understand there are two places where a realm can be chosen, your army can be from a specific realm, and then the battle is fought in one of them. So here are my questions. 1) The realm where the battle is fought is currently determined by a dice off before the game, correct? 2) There are 4 things that are determined by realm, an extra spell all wizards know, an available magic item, a terrain feature, and a command ability. Which of these is determined by where the fight occurs and which by where your army is from? Thanks!
Choosing a realm for an army to be native to only allows you to take the Realm's artefact as an option. Playing in a realm battle grants wizards access to the spell list. Heroes/Generals access to the realm command ability. And all terrain gains the realm scape feature. The realm of battle is determined by a dice roll. Most events have been pre-selecting realms of battle however. The rules are detailed in both Malign Sorcery and GHB2020.