If you haven't already, buy the expansion. (You can buy the expansion early and do lots of prep work before killing Mazuriel if you like. However to beat the expansion, you will have to kill him eventually.)
You need to retrieve the dragon egg from the Ridge Fault and put it in the lava in the locked room in the SE corner of the abandoned tower basement.
You need to build a Dragon Caller. Best choices are probably
1) a converted 99% Master Thief Rogue with 24 INT and 40 LCK (if you like to be able to pick locks and cast spells with impunity while hidden), or
2) a converted Monk with 24 INT and 40 STR (if you like doing tens of thousands of points damage with a single swing), or
3) if you really like to grind, both.
Visit the Dragon Grave in southwestern Watertop for a Firestaff for one of your Arch Mages and the Armageddon spell for all of your casters.
Best single combat grinding is probably the Creepers and Elder Creepers fixed encounter in northwestern Watertop. This is a hard battle, but once your Arch Mages and DCs have Armageddon, it is manageable in about four rounds.
If you haven't already, go to the Ridge Fault and retrieve the Dragon Egg. You have to be carrying the Stone Sword, but it does not have to be equipped, to get past the ancient force. To get to the Dragon Tower you need to make a leap of faith and walk on air to the Tower. The answers to the riddles are
Best circular grinding is probably the old Bonehouse in Shadows of Mar, which is reached by going from Watertop to Iron Valley to Crystal Sea to Tranquil Grove to Shadows of Mar (whose link point is called SWAMPS). I like to set a beacon at the entrance to the old Bonehouse and another 3 steps east of the creeper encounter in Watertop. I also have one in Castle Cranbourgh near the review center.
Now you need to explore the six levels of Miners' Deep. Get there using the trains near the entrance to Karilan Andur. On the first level you can find some Gloves of Force for one of your casters. You need to go down to the sixth level to meet the ruler of the mines
South East of the Watertop camp is the Dragon Grave where you learn you need the tokens of good and evil. Your casters can also learn Armageddon for 100,000 each Below the Dragon Grave.
In the Northwest part of Watertop there is a place to find a battle song for your bards. To get there you will have to battle through a fixed Creeper and Elder Creeper battle that will take about 16 Armageddon level attacks. Then you'll have to face prowlers and a shadow stalker that require silver+ round enhanced weapons. These are tough battles before you can find the prize.
To the North of Watertop you find Iron Valley. To the East of the path North through the valley you can explore Dunkelloch. After fighting the monster itself, you can find the Assassine, a great weapon for your rogue.
Northward along the path you meet the Prowlers & Shadow Stalker encounter. The Thylacines that accompany them are pretty easy. You can take them out with magic. You have to defeat them all to proceed. And the rest require Runed weapons of Silver or better to hit for damage. It seems to take about 40,000 points of damage to kill the shadow Stalker and something like 8000 for each Prowler. You can easily spend an hour real time on this battle. Save right before it if you are not in legend mode.
After the battle proceed North and across the bridge. Just to the South across the bridge you meet two wounded people Elena asks you to take back to Watertop. You have to have two slots open for them so drop two of your band back at the camp in Watertop. Your guests will leave right outside the camp, and give you two hints when they leave:
Visit the four corners of Crystal Sea and get the Dragon Scales after fighting the 4 Ancient Oaks. The scales are each in an urn, marked by blue pluses on the map.
Before visiting the dragon at the gate to the planes in the middle od the Crystal Sea, you'll want the Unicorn Heart from the structure in the SouthEast part of the Tranquil Forest. This Balances nicely with the Black Heart you got from the Chamber of Storms.
While in the Crystal Sea you can fight the Pirates in the North central part, but it probably is not necessary to "beat" the expansion. Defeating the Pirates will get you the codes for maintenance mode that you need in the Silvertop Mountains placed into your log, but they are revealed in this walk thru a little later.
Travel on North to the Shadows of Mar. In the basement of the Old Bonehouse you'll find the Axe of Souls and get the Spirit Condenser from the necromancer. You need to know Ignaz is buried by the Castilla Artonsa to get to the Fisher of Souls on the top level. The Fisher can be a tough battle; he drops the Dragon Key when you defeat him.
You can find the Cap of Resolution in the SouthWest part of ths Shadows of Mar, but it is probably a downgrade from the helm your each of your casters is wearing. However it does seem to have the added unlisted attribute of increasing spell points by one per round like the gloves and ring of force. And the experience does teach you how to deal with a similar situation later where the way through a trap is to use the Guardian Angel or Guardian Spirit spells.
Time to use the spirit condenser. Find 13 graves. Stand facing each and use the condenser. If successful you'll get a spirit essence in your inventory. There is 1 in the SE corner of the Shadows of Mar. There are 3 outside the temple in SW Watertop. There are 2 in the Lost Temple in Druids Grove. There are 4 outside the Forgotten Crypt you entered early in the game. There are at least 3 near the crypt where Ignaz is buried in Artonsa. Once you have 13 Spirit Essences head to the castle in the Coastlands to meet Master Mortifer.
At the tower, after it says to use a device, touch the door. Then use the Spirit Condenser. Then touch the door again.
Mortifer tells you to see his Apprentice for a reward. The Apprentice says see his nephew Digger in the Silver Mointains where nature was unleashed.
On the Silver Mountains
Apparently after you visit Chuan and then visit the shrine in Silver Mountains South due South of the water and then return to Chuan in Silver Mountains just SouthWest of the NorthWestern water, he gives you a Mithril rune and you can get combat stance training in the brown area of Silver Mountains. (You might be able to do this sooner, but that was when I noticed I could get the training.) Actually you can learn the stances after dragging your baby dragon to the Guardian of the Planes.
In Digger's house on the Silver Mountains Top use the circular gadget to open the chest past the two new watchdogs to get a firestaff. If you have visited the Apprentice you can follow the path West from his rooms to the Volcano. South of the chest in a hidden area you meet a Kobold who wants 4 cog wheels, a circular thingy, and a red lens. He'll give you a disruptor.
Back in the SE corner room of the Gateway to the Planes you meet Maelin who will trade you a Shield of Refraction for your 4 Dragon Scales.
Cast Dragon Flight and enter the Plane of Air. From here on it's wise to have Guardian Angel active. When you get to the brown path you might want to activate Heart of Asphgyr. You'll be hit by a north wind that severely drains you. You can recoup one step West of where the wind hits you. When you're ready proceed to a battle with an Efreet. Then take on Arsyth. He'll drop the Key of Water when he dies.
That means visit the Plane of Water next. Enter from the Gatway to the Planes.The light blue squares are acid traps, but you can survive them especially with Heart of Asphygr active. Fight Asphgyr in the central square area. When you win, he'll drop the Key of Fire.
Use an East-West passage in a wall south ou the central square to access the doors to the Plane of Fire. Proceed South to the central square and fight Bonfyr. Bonfyr can only be damaged with weapons so save your spell points for healing. You need Guardian Angel active and refresh with Guardian Spirit so you are ready when/if Bonfyr goes berserk. Bonfyr drops the Key of Earth.
There is a passage through the Southern part of the West wall of the central square. It's probably easiest to get there from the Plane of Air. If you instead come from the Gateway, circle around the central square counter clockwise through the darkness where almost every square is a spinner and there are lots of traps that Stone members of your party. The walls in the central square move, so be patient and you can work your way to the final Dragon, Cretor. After this battle you get the Key of Air, which you will need to open a door to get to the Command Center.
From the Gateway, enter the Plane of Fire. Proceed South towards the door. Before entering throw the lever SouthEast of the door. Now go through the door and West across the lava. Use your Key of Air to open the door you reach after the lava. Circle counter clockwise to the South and throw the second lever. Go North to the star on the map and place the Disruptor. Proceed West to the Command Center. Check that Guardian Angel is on. Place the Shield of Refraction on it. Back away and restore your health and Guardian Angel spell. Proceed to the nose of the ship. With text running so you can see the battle it takes about 15 minutes to kill the Deflier and his 160 Viruses. I had little trouble killing them with my party of 5 DCs who were Rouges, 1 DC who was a Monk and a single Arch Mage -- all 25th level in Legend mode. You will probably need to use one of the Emergency exits (levers) at the Southern end of the ship to get off the ship and receive Mario's thank you message.
Thank you Mario for an awesome expansion.