Guys, please, specify Era/Mods version, when you ask something, because a generic anwer for all versions may not exist.
Archer30, it's not released, but I hope will be released today or tomorrow.
https://dropmefiles.com/Msmgs
From this version one can safely use !?BR (prefer to use named !?FU(OnBattleRound) version though), !?FU(OnBattleRound) or even !?FU(OnCombatRound). All 3 triggers are the same. All occur in visible rounds only. In all of them v997 is valid round number. For all of them Tactics phase starts from -1000000000 round. For all of them the first non-tactical round starts from 0 and has no duplicates.
As you know, in WoG round 0 can occur twice, round -1 depends on tactics, tactics has negative DECREASING round numbers, so it's a great buggy mess.
Valery, selecting creatures in tactics phase is "WoG Native Dialogs" harmless feature. We need mods/versions/savegame to give more information.