The Veldt
The Veldt has a new look. It is now a broken island scattered with wastelands, but the mechanics of the battles here has not changed. Getting Gau back in the party is as simple as fighting with three or fewer Characters until he appears after a battle. He will learn Rages from the battle he returned after as normal, but does not automatically gain any other new Rages from his time since the Floating Continent.
Cave in the Veldt
There is a new cavern accessible on the Veldt, replacing Crescent Mountain. There are several nice Treasures to find here, and you will be able to follow Interceptor to rescue Shadow, who is injured. (If you did not save Shadow on the Floating Continent, Relm will be here instead.)
There are only two types of enemies in the Cave in the Veldt. Almost every battle is against one or two Toe Cutters. They have a moderately powerful attack and will counter your attacks with Doomsickle, which drains HP. They absorb Ice but are vulnerable to both Fire and Wind. Keep your HP up between battles and they should offer little threat.
In rare cases, you'll instead be confronted with a Rhyos. If you keep the battle short, you only need to deal with their powerful basic attacks, which they also use as counters. On the fourth round, however, they will go berserk, starting with the double-damage Rage special and immediately following it up with three Abilities targeting the whole party. These can include Blizzard, Fire Ball, Giga Volt, Magnitude8, and Aqua Rake. Of these, Giga Volt is the most dangerous, though Aqua Rake and Magnitude8 can also dish out a lot of damage.
Navigating the Cave in the Veldt
The Cave in the Veldt is a small but complicated area, similar in some ways to Umaro's Cave. You enter via the West Cavern, which has two passages, one in the north and one in the south. The southern path leads to a dead-end plateau, so head north to start. You'll cross a stone bridge where you'll see a chest containing the Rage Ring for Umaro. Further east is a campfire surrounded by four thieves. They explain that Gau will not approach a full party, but you should know that from experience anyway. One mentions a "frightful dragon" in a forest north of the Veldt, which may refer to World Map Dinosaur Island. That doesn't really fit with the rest of his dialogue, but it is a location worth noting as it's a fantastic place to level—if you can survive.
The door to the north is the only path onward. After passing through it, you'll soon reach a three-way tunnel. It will take some maneuvering to get to the room to the west, which has a chest containing the Tiger Fangs. To get them, you'll need to first defeat Allo Ver. This is an interesting Monster that uses Doom and Condemned to try to Wound your party members. It can counter attacks with Doom as well. If the battle goes on for about a minute, Allo Ver will use Atomic Ray eight times in a row, likely destroying the party unless someone is protected from Fire. You should be able to cut through its 8,000 HP long before that happens. Allo Ver is both human and undead, with the standard undead weaknesses to Fire and Pearl.
Make your way to the southern tunnel of the three-part intersection. This leads to a path under the stone bridge you crossed earlier and further down into the dungeon. You'll see three rocks blocking a passage to the east, and a door to the south. There's a switch near the door which will open a path through the rocks, but don't miss the Striker in the chest down the stairs to the south. The previously blocked path leads to a new room where you'll see Interceptor and Shadow (or Relm) on a plateau above you. You can't reach them just yet, so continue on, climbing the stairs to the north. There's a save point in the next room, just in time for a boss battle. As soon as you enter the southwestern doorway, you'll be drawn into a battle against the SrBehemoth.
SrBehemoth
This is a two-part fight, and you're technically fighting two different Monsters. First is the blue SrBehemoth, which will start the battle with combinations of Pearl, Ice 2, Ice 3, and basic attacks. Once you've dealt at least 8,760 damage to the Monster, its attack script will add Meteo to the rotation. The SrBehemoth will counter Pearl or Flare with Meteo as well, and counter other offense with basic attacks. It will also respond to attempts to use Reflect by dealing damage and removing it with Evil Claw. You can turn the SrBehemoth into an Imp, but it will respond by doing double critical attacks for several rounds before removing the Status.
With 19,000 HP, this battle may take a while. Fire and Poison are both effective, though the SrBehemoth absorbs Ice. Its magic attacks are powerful and this battle is immediately followed by another tough one, so make sure to keep your party's HP high.
When the SrBehemoth is defeated, it will fade away and you will be attacked from behind by a second, undead SrBehemoth. Even though this looks like a back attack, your Characters rows are not affected by the change. This version of the SrBehemoth will still use basic attacks as counter, but no longer counters Pearl or Flare specifically. It will cast Doom and Meteo, but it also has access to a special combination. It will use Hypno Gas to inflict Psyche on a Character, then follow up by attacking that Character four times in a row.
The undead SrBehemoth has the same 19,000 HP as the original, and the same weakness to Fire. This one now absorbs Poison but has gained a vulnerability to Pearl and no longer absorbs Ice. Once defeated, the SrBehemoth will drop a BehemothSuit, the best costume Strago and Relm can wear and arguably the best body Armor in the game. You can earn more of these by fighting SrBehemoths on the Veldt and wager extras at the Colosseum for another powerful body Armor, the Snow Muffler.