The goblins eyed Moody with a great deal of apprehension, and not without reason, Neville found. Unlike the last dozen wizards passing underneath the green sparkles of the thief's downfall, Moody did not have a single yellow burst surrounding his wand. He was instead covered in a glorious crimson.
His hip flask was removed as a goblin whispered "polyjuice." A small package was taken from under his cloak, "classified, list B." A dozen knives were drawn from his left boot, made from different metals. Likely silver, cold iron, gold, and ironwood. An acromantula leg was untangled from around his waist. And after some significant difficulty a six inch long tooth was extracted from... Neville couldn't exactly tell where. It looked like his bottom, but there wasn't any opening there for them to have pulled it out of.
The goblins whispered a very quiet question to him then, to which Moody responded with a large grin and a small nod, and one goblin ran off with the tooth, returning moments later with a large, sealed box.
The goblins eyed Moody's eye, and it eyed them back for a few tense moments, and they eventually settled for just confiscating his wand.
Walking him through the thief's downfall again, Moody still blasted a vibrant red from his eye, but the rest of his body cooled to a yellow not much more dangerous than most wands, and the goblins conferred among themselves and seemed to decide that this was the best they could hope for.
A few minutes later, Neville and Luna entered Gringott's. No need to formally announce their connection to Moody and subject themselves to further scrutiny.
Neville's whole body tingled with a yellow verging on orange, as bring as his wad, and a goblin raised one eyebrow while consulting some kind of chart, then whispered, "congratulations," and let him pass.
Luna's entire body was such a calm green it was almost blue, and the suspicious goblins made her pass through three times, the third time while actively brandishing her wand. When the thief's downfall reused to identify even this with anything closer to yellow than an earlier customer's pinky toe they agreed she must be harmless.
When they provided their keys they were hustled onto the same cart as Alastor, and Luna's wand was in his hand so soon after they were out of sight of the office that Neville thought it was magic for years before Alastor deigned to teach him muggle sleight-of-hand.
Once Moody had a wand, it was a simple enough matter to imperius the driver and find their way to the correct vault number Lily had obtained from Snape. He also managed to unlock what he revealed was a basilisk tooth from what he explained was a safe deposit package for storing magical weaponry.
What would actually be difficult, Moody continued, would be getting back out.
Moody cast a wide variety of charms and still insisted Neville shift into his animagus form after the goblin unlocked the cell. Then Neville, now a disillusioned, hovering, ray-shielded, silenced, shrunk, nondetectioned, charmed-to-appear-dead, charmed-to-appear-nonmagical, charmed-to-detect-as-a-snake Lion with a basilisk tooth held very carefully in his jaws, floated into the room.
Moody's eye easily identified Helga Hufflepuff's cup in the packed piles of brass serving dishes, cutlery, and knick-knacks.
Neville floated slowly over to it, then in one quick motion drove the tooth into the cup. He hesitated momentarily, mourning the destruction of one of Helga's last heirlooms, who had not been evil and deserved to be remembered, before he was puled forcibly out of the vault by a gesture from Moody. Brass exploded behind him, a torrent of metal which might have threatened to drown him or beat him to death had he stayed a moment longer. Neville gave a quiet gulp as the imperiused goblin closed the doors behind him.
"No time for that sentimental reverie, Longbottom. CONSTANT VIGILANCE! They'll have noticed the ruckus," Moody snapped, and and they began to move along a different path in the cart. "We're taking the express route this time, which means we'll be passing a dragon. I'll take care of the flames, Lovegood watch that the cart keeps going. Longbottom, watch the jaws and claws. It's coming up, and..."
All Neville remembered of the encounter was a raging wall of fire surround them and washing barely past the sides of the cart, an intense load of adrenaline so powerful it gave him nightmares, and constant movement.
When he finally returned to human form his body reminded him of somewhat more in the form of dozens of bruises and gashes adorning every corner of his body, though at least he didn't see any on anyone else. Luna took her wand back and muttered words that he couldn't hear but which kept him from falling unconscious.
"I'll have your wand now, boy, and Luna hers. We've done well so far but we're just getting to the difficult part." Moody steeled himself and began piling up defensive charms at an alarming speed.
But when they emerged into the entrance hall of Gringott's they did not find a legion of armed goblin soldiers. They found instead a warning beacon blaring unattended, and a large sign saying "Gringott's will be closing without notice due to the expiration of the treaty of Nurmengard." As they stepped into the room they saw one more thing. A banner, prominently displayed on the wall, showing a live, annotated picture of the Ministry of Magic. Showing the court of the Wizengamot, and the seat of the supreme mugwump. And in that seat, unmistakable, the Dark Lord Voldemort.