diff --git a/src/ChatCommands.cc b/src/ChatCommands.cc
index 4593f7bb..78016ea6 100644
--- a/src/ChatCommands.cc
+++ b/src/ChatCommands.cc
@@ -1224,6 +1224,41 @@ static void proxy_command_item(
   }
 }
 
+static void server_command_enable_ep3_battle_debug_menu(
+    shared_ptr<ServerState>, shared_ptr<Lobby> l, shared_ptr<Client> c, const std::u16string& args) {
+  if (!c->options.debug) {
+    send_text_message(l, u"$C6This command can only\nbe run in debug mode\n(run %sdebug first)");
+    return;
+  }
+
+  check_is_game(l, true);
+  check_is_ep3(c, true);
+  if (l->episode != Episode::EP3) {
+    throw logic_error("non-Ep3 client in Ep3 game");
+  }
+  auto base = l->ep3_server_base;
+  if (!base) {
+    send_text_message(l, u"$C6Episode 3 server\nis not initialized");
+    return;
+  }
+  auto server = base->server;
+  if (!server) {
+    send_text_message(l, u"$C6Episode 3 server\nis not initialized");
+    return;
+  }
+
+  if (!args.empty()) {
+    server->override_environment_number = stoul(encode_sjis(args), nullptr, 16);
+    send_text_message_printf(l, "$C6Override environment\nnumber set to %02hhX", server->override_environment_number);
+  } else if (server->override_environment_number == 0xFF) {
+    server->override_environment_number = 0x1A;
+    send_text_message(l, u"$C6Battle setup debug\nmenu enabled");
+  } else {
+    server->override_environment_number = 0xFF;
+    send_text_message(l, u"$C6Battle setup debug\nmenu disabled");
+  }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 
 typedef void (*server_handler_t)(shared_ptr<ServerState> s, shared_ptr<Lobby> l,
@@ -1256,6 +1291,7 @@ static const unordered_map<u16string, ChatCommandDefinition> chat_commands({
     {u"$i", {server_command_item, proxy_command_item}},
     {u"$kick", {server_command_kick, nullptr}},
     {u"$li", {server_command_lobby_info, proxy_command_lobby_info}},
+    {u"$ep3battledebug", {server_command_enable_ep3_battle_debug_menu, nullptr}},
     {u"$maxlevel", {server_command_max_level, nullptr}},
     {u"$minlevel", {server_command_min_level, nullptr}},
     {u"$next", {server_command_next, proxy_command_next}},
diff --git a/src/Episode3/DataIndexes.hh b/src/Episode3/DataIndexes.hh
index 1298f073..e9ee7b4d 100644
--- a/src/Episode3/DataIndexes.hh
+++ b/src/Episode3/DataIndexes.hh
@@ -794,27 +794,38 @@ struct MapDefinition { // .mnmd format; also the format of (decompressed) quests
   // - The color of the battle tile outlines (probably)
   // - The preview image to show in the upper-left corner in the map select menu
   // The environment numbers are:
-  // 00 - Unguis Lapis
-  // 01 - Nebula Montana (1)
-  // 02 - Lupus Silva (1)
-  // 03 - Lupus Silva (2)
-  // 04 - Molae Venti
-  // 05 - Nebula Montana (2)
-  // 06 - Tener Sinus
-  // 07 - Mortis Fons
-  // 08 - Morgue (destroyed)
-  // 09 - Tower of Caelum
-  // 0A = ??? (referred to as "^mapname"; crashes)
-  // 0B = Cyber
-  // 0C = Morgue (not destroyed)
-  // 0D = (Castor/Pollux map)
-  // 0E - Dolor Odor
-  // 0F = Ravum Aedes Sacra
-  // 10 - (Amplum Umbla map)
-  // 11 - Via Tubus
-  // 12 = Morgue (same as 08?)
-  // 13 = ??? (crashes)
-  // Environment numbers beyond 13 are not used in any known quests or maps.
+  // 00 = Unguis Lapis ("BONE")
+  // 01 = Nebula Montana 1 ("ALPINE")
+  // 02 = Lupus Silva 1 ("FOREST 2-1")
+  // 03 = Lupus Silva 2 ("FOREST 2-2")
+  // 04 = Molae Venti ("WINDMILL")
+  // 05 = Nebula Montana 2 ("ALPINE 2")
+  // 06 = Tener Sinus ("COAST")
+  // 07 = Mortis Fons ("GEYSER")
+  // 08 = Morgue (destroyed) ("BROKEN MORGUE")
+  // 09 = Tower of Caelum ("TOWER")
+  // 0A = ??? (crashes) ("MAPMAN")
+  // 0B = Cyber ("CYBER")
+  // 0C = Morgue (not destroyed) ("BOSS")
+  // 0D = (Castor/Pollux map) ("REAL BOSS")
+  // 0E = Dolor Odor ("STOMACH")
+  // 0F = Ravum Aedes Sacra ("SACRAMENT")
+  // 10 = (Amplum Umbla map) ("RUIN")
+  // 11 = Via Tubus ("METRO")
+  // 12 = Morgue ("NORMAL MORGUE")
+  // Environment numbers above 12 are replaced with 0B (Cyber) if specified in
+  // a map definition. The following environment numbers are used internally by
+  // the game for various functions, but cannot be specified in MapDefinitions:
+  // 13 = TCardDemo (sends CAx14 and CAx13, then softlocks at black screen)
+  // 14 = crashes
+  // 15 = crashes
+  // 16 = Battle results screen
+  // 17 = Game Over screen (if used online, client disconnects without saving)
+  // 18 = Episode 3 staff roll
+  // 19 = View Battle waiting room
+  // 1A = TCard00_Select (debug battle setup menu)
+  // 1B = nothing (softlocks at black screen)
+  // TCard00_Select is accessible on newserv with the $ep3battledebug command.
   /* 000A */ uint8_t environment_number;
 
   // All alt_maps fields (including the floats) past num_alt_maps are filled in
diff --git a/src/Episode3/MapState.cc b/src/Episode3/MapState.cc
index ce37b38b..d48646e2 100644
--- a/src/Episode3/MapState.cc
+++ b/src/Episode3/MapState.cc
@@ -38,7 +38,7 @@ void MapAndRulesState::clear() {
   this->map.clear();
   this->num_players = 0;
   this->unused1 = 0;
-  this->unused_by_server = 0;
+  this->environment_number = 0;
   this->num_players_per_team = 0;
   this->num_team0_players = 0;
   this->unused2 = 0;
diff --git a/src/Episode3/MapState.hh b/src/Episode3/MapState.hh
index 1c78f7aa..8ffcb3ee 100644
--- a/src/Episode3/MapState.hh
+++ b/src/Episode3/MapState.hh
@@ -25,7 +25,7 @@ struct MapAndRulesState {
   MapState map;
   uint8_t num_players;
   uint8_t unused1;
-  uint8_t unused_by_server;
+  uint8_t environment_number;
   uint8_t num_players_per_team;
   uint8_t num_team0_players;
   uint8_t unused2;
diff --git a/src/Episode3/Server.cc b/src/Episode3/Server.cc
index 80a47b5c..5b7de22a 100644
--- a/src/Episode3/Server.cc
+++ b/src/Episode3/Server.cc
@@ -66,6 +66,7 @@ void ServerBase::recreate_server() {
 Server::Server(shared_ptr<ServerBase> base)
     : w_base(base),
       tournament_match_result_sent(false),
+      override_environment_number(0xFF),
       battle_finished(false),
       battle_in_progress(false),
       round_num(1),
@@ -1841,6 +1842,11 @@ void Server::handle_6xB3x13_update_map_during_setup(const string& data) {
       (this->registration_phase != RegistrationPhase::BATTLE_STARTED)) {
     *b->map_and_rules1 = in_cmd.map_and_rules_state;
     *b->map_and_rules2 = in_cmd.map_and_rules_state;
+    if (this->override_environment_number != 0xFF) {
+      b->map_and_rules1->environment_number = this->override_environment_number;
+      b->map_and_rules2->environment_number = this->override_environment_number;
+      this->override_environment_number = 0xFF;
+    }
     b->overlay_state = in_cmd.overlay_state;
     if (b->behavior_flags & BehaviorFlag::DISABLE_TIME_LIMITS) {
       b->map_and_rules1->rules.overall_time_limit = 0;
diff --git a/src/Episode3/Server.hh b/src/Episode3/Server.hh
index dfcd9d4b..d43f6ea9 100644
--- a/src/Episode3/Server.hh
+++ b/src/Episode3/Server.hh
@@ -247,6 +247,7 @@ private:
 
 public:
   bool tournament_match_result_sent; // Not part of original implementation
+  uint8_t override_environment_number; // Not part of original implementation
 
   uint32_t battle_finished;
   uint32_t battle_in_progress;