I didn't really notice Bring Out Your Dead on my first few playthroughs of Torchlight 2. It's a side-quest tucked snugly into the game's first act, and it's typically pulpy stuff. Meet a shady character near Skull Hollow, chat for a bit, and then head deep inside the catacombs of the Bone Gallery to fight Mordrox, a giant zombie troll.

It made more of an impact on my latest playthrough, mind, and that's because of the aftermath of that final battle. Mordrox had been hammered into oblivion, his skeleton guards were blasted into powdery white gravel, and, looking about, I noticed the floor was knee-high with loot. More loot than I'd ever seen in Torchlight 2 before: full knee-buckling inventories of the stuff. Shoulders, hats, trousers and various wonderfully nasty weapons; potions, spells, piles of glittering gold.

Torchlight 2's a generous game, of course, but something funny was up. Or rather, something funny had been installed. On my most recent playthrough, I've been exploring Torchlight 2 alongside SynergiesMOD, a total conversion that makes quite a difference to the way that the action RPG unfolds.

At first, though, I had a hard time pinning down exactly what had changed. The thing about modding an action RPG - a game that's already designed to throw massed varieties of crazy stuff at you every few seconds - is that it can be tough to disentangle what's new and what's just glorious randomised business as usual. Did the fixed overworld map always take this weird right angle turn just before that town? Did the tile-sets for the first dungeon always look so grim and gothic? Is this warbeast thing with the eyes that glow like the Scarecrow's do in that bit at the end of Batman Begins a brand new critter, or just one that never bubbled out of the algorithms for me before?

If this image doesn't do much for you, Torchlight 2's probably not your game.

Bring Out Your Dead is where it truly clicked. Synergies adds plenty of new wrinkles to Runic's game, but what it does really energetically is change the pace - and that shines through most clearly in a tightly controlled dungeon. Torchlight 2's never been short of enemies, but now you pretty much wade through them, smashing dozens of the blighters every second or so even in the quiet moments and facing off against elite baddies with alarming regularity from the first spawn onwards. It's like fording a big thick swamp of monsters - and it's brilliant.

Oh, yes, and there's a new class, too, and that provided the focus for a pleasant day's antic clicking as I tried to spot what else was different. Necromancer's the name, and summoning's the game: you can yank zombies out of the ground to fight alongside you, you can conjure death dolls and flaming infernal scourges, and you even get the chance to call in a massive ghostly dragon to walk in your footsteps when the going gets really tough. Other trees explore curses and various shades of bone-based trickery - skeleton hordes or the ability to send bone spikes juddering through the floor, sir? - and the main show-stopping skill is called Skull Barrage, which sees you blasting out multiple purple things - skulls, I would fancy - that then radiate, smacking into enemies and piling on the necromancing hurt. Oh yes, and if you shuffle through the new character creation options a little, you'll discover you can have a ghost as a pet. A big ghost with heavy chains to rattle and swing. He's quite a guy.

When I caught up with Salan, the defining force behind Synergies, to discuss his work on the mod, the Necromancer was the thing I was most eager to hear about. Synergies itself comes across with all the glorious, unpredictable energy of a work in progress - which it is, of course - but the Necromancer already feels whole.

"I played the Berserker and Embermage from level one to 100 and into the far reaches of the new game ranges," says Salan when asked what inspired the character. "My wife played the Outlander and I ignored the Engineer. When I decided on the Necromancer I had originally wanted to make the Warlock first. But the Necromancer was a name any single ARPG fan knows and loves. It was also something we were missing from Torchlight 2: a true pet caster. I designed the class with a mix of spell attack types to allow the player to customize himself in different directions as per his own desires. The Skull Barrage, Bone Needles, Bone Spikes and Infectious Touch are so radically different from each other that they each play to a different style of players desires, and you also have the ground clutter spells and utility spells of the like that round out your choices as a caster.

Skull Barrage! It helps if you shout its name as you use it.

"I then wanted to achieve the same thing with the Necromancer's monsters," he continues, the design details getting him warmed up. "11 different monster summons are available with the Necromancer, and each of them are designed to be completely different in application and style. The skeletons and zombies both spawn their full amounts for instance. The zombies are slow and will need to be summoned at the start of fights to be truly useful, but at end tiers they syphon life to their master. The skeletons are more tanky as they level up. Death Dolls and Spores both use spawn classes for spawning. What that means is you'll get different amounts of each every time you cast the spell, but you get more of them overall. The fiend spell runs off of enemy corpses, and will expand itself. The fiends of the fiends won't follow you, and all fiends have a lifetime that runs out and desummons the monster. That's not even touching the master minions that each have a buff that affects themselves and the horde minions under your control. And of course everyone forgets the bone wall half-skeletons. Bone walls are boring, but a bone wall that sheds half-skeletons is just cool, why not throw that in there?"

Tanky skeletons, the fiends of the fiends, oddball words like 'desummons': there's a poetry to this kind of creative meddling. It's a focused kind of poetry, too. Ghosts as pets, the ability to summon dragons? Synergies understands that, after your first few playthroughs, your typical ARPG player is like one of those flesh-mound gourmands brought in on the latter stages of Masterchef. You know, they've tried the best, they've tried most of everything else along with it and now they're jaded and burnt out and prone to the sad sweats. They're in desperate need of crazy excess to bring their senses back to life. That's where people like Salan come in.

"All of my friends in high school went into computer programming," explains Salan when accounting for his strange tinkering passions. "We were the kids who loved the data processing, the marketing and the computer science classes above the other fun things like math and woodworking. I never pursued the field in college, but I was always the individual in my group who created new things for us to do, rather than just replaying the game's original content over and over again."

Synergies is not Salan's first mod. "The biggest project from the past would be editing for a Company of Heroes mod," he remembers. "I started out as being a passionate player and strong advocate in the community itself. At the end of that experience I had created my own full conversion mod called FallofFrance. I had implemented a dozen extra nations, reworked the balance point completely and reworked the gameplay to be nothing like vanilla or even the mod I had been working on previously. What I've come to realise is, with my history and desire, when it comes to modding it's simple: I want to change everything and recreate my own vision of it. So far its worked well for me."

More classes - and another overhaul to the end-game - are still to come.

Is that what happened with Synergies, then? A little idle coding turned into something more elaborate? "I wanted to recreate what I liked about my past ARPG experiences, MMO experiences, personal creations and just flat out dreams," says Salan. "I loved how Titan Quest did skill pages, and the name of the mod is directly in relation to that. I want to make a class where I take every skill page created, and give the player the in-game ability to complete quests and have those quests decide which skill page is assigned to the player. Allowing you to customize your character from every page available means you can have synergy in your choices. And so the mod's name was born.

"Beyond that decision I started tinkering," he continues. "I wanted more monsters, I wanted fights that last a few minutes instead of a few seconds. I hated in Titan Quest how I could go up to the end boss and the fight would be over in 15 seconds, so one of the first things I did in the early versions of Synergies was messing with spawn classes and monster health and damage ratios. From there, it was one step after another. Constant evolution. Developing a mod like this is a challenge, and to date I am the only one doing it for Torchlight 2 on anywhere near this scale. It's difficult going from item creation to monster creation to raid creation to class development to planning new and invigorating ways of implementing all of them. I have to go in like-minded spurts. It's basically retraining your brain each time to think from a different perspective. I think it helps though, because in the end I know everything about the environment and what to expect from the changes I make in each section. The time I have put into this mod is basically incalculable. I work, I have a family, and I mod. I get a quiet day at home, I mod. When everyone is in bed I stay up late and mod."

He's not working alone, of course, and he's eager to reel off friends who have made significant contributions. "Kelintor has been incalculable for being able to do a few of the things I have been able to do so far," he says. "Quests? While I was close to getting it done, Kelintor broke the ground on them and helped me with a tutorial on how to make them work correctly. He made a money-changer mod which I expanded on, and a portal mod which I also expanded on. Then he in turn went back to and perfected both. He made mercenaries that I used while waiting to make my own and various other odds and ends that I have incorporated. Recently I reached out to Epoch as he was making a Ninja class and I have helped give him a much broader horizon of feedback with making his mod usable with Synergies. I have enjoyed the back and forth discussions with them both and the extra help with finding bugs that were eluding me."

Mods and ARPGs go hand in hand - except for the case of Diablo 3, of course.

Synergies does some wonderful stuff to the main campaign, but it's really only just getting started. Reach the end-game, and you suddenly get dungeon chains perfect for raiding, and all kinds of new loot. This stuff requires a very high level in order to enjoy it, of course, but it offers some of the most spectacular battlefields you'll see in an ARPG.

"In the end game I would say [Synergies' major changes involve] moving the character between newly hitting level 100 into the raids themselves," explains Salan. "I made an area called Table Mountain with this idea as its goal. I can only farm levelling areas so many times before I get bored of it, and I can't expect anyone to want to do this in a mod after having done it enough times in vanilla Torchlight 2. So I created a whole area to help progress into those raids. This area is still in its first phase, with another phase planned. Phase 2 will see everything in Table Mountain vanish and it'll be replaced by quest givers. In order to access these removed NPCs you will need to finish the quest associated with them. The raids themselves present tiered challenges with legendary armor and weapons as rewards. Farming a raid to get the upgrades allows you to progress through the tiers, and the difference in the fights themselves are well balanced."

It's a staggering amount of work, even before you realise Salan's been toiling away without GUTS, Runic's official modding tools, which have yet to be released. "We have community-made tools to unpack PAK files and DAT files into TXT files," he shrugs. "And we have a community-made layout editor that has more than two thirds of its entries listed as 'unknown entry'. I unpack everything and edit text files. Following the threads of one link to the next can be insanely hard, but as you can see by the end result, it's extremely rewarding."

Even with so much content left to implement, Torchlight 2's developers have already been taking an interest in Synergies. "Runic has been great," says Salan. "There's a post in the development thread on their forums where one of the devs asked for a copy of my files. As this mod is so extensive it's being used behind the scenes for some of their GUTS integration. I've had a few hearty words from Runic's president, Travis Baldree, on it being a great mod. They have been super supportive in the limited exchanges I have had with them."

It will be interesting to see how much Synergies changes once GUTS is released.

And the community? "That's 95 per cent insanity over how elated they are by having the mod available, and the odd five per cent elitist mindset that I am ruining their lives by some of the decisions I have made," says Salan. "I'm passionate and involved in the mod and the forums. I listen to the critiques and reply about decisions and why I made them. If something is pointed out that I might not agree with but can understand, I try to listen with objectiveness, and in all honesty it has shaped a lot of minor decisions I have made. But I'm very strong willed and willing to stick to my designs."

Synergies is currently in version 1.50B, and Salan shows no signs of stopping. "My latest patch? Oh man. I just finished doing the mercenaries finally. Sadly this means that Kelintor's champion mercenaries will see their last sunshine but these mercenaries I am making are all humanoid, wearing legendary armor and legendary weapons and each one is named after a community member. They are strong, and they're meant to be end-game companions for solo and group play. With the next patch I release the start of a new class, the Paladin. I've put it off for other priorities long enough. It's time to get it out. The Paladin will use the Engineer charge bar, and will be based on synergetic attacks that buff and debuff the player into a balanced theme of interaction. Its not your typical Paladin theme, but this will be an adventure that will likely take me a month to see through in the least."

As for the time being, Synergies has already been downloaded over 110,000 times - an amazing achievement considering it's around six months old and has been made with limited tools. "I will continue with the passion I started with," says Salan, wrapping things up, before adding that he's currently on the lookout for an artist to join the team. "This mod is going nowhere but up," he says. "Come check it out while you have the chance to potentially tailor its journey, even if just a little."