To truly excel at Multiplayer seems to require the following.
Choose Helheim at the nation select screen.
Roll over nearest opponent if you can do so swiftly without compromising research and progress.
Research and cast a gem producing spell.
Research and cast forge of the Ancients.
Forge as many of the unique items as you can.
Research and cast as many of the king/queen elemental spells you can.
Create as many banelords as possible.
Raid with glamour units and squash armies with Banelords and equipped elementals.
Ally with 1 sea nation.
Done.
Before anyone gets upset, this post is more fact than farce. I am in one game where the Helheim player is dominating, and this seemed to be his path, except that he squashed two nearby players early with Helherdings.
In two more of my games, it is a bit early, but the spells have been cast in pretty much the same order as listed above. I am playing a water nation in both those games and I have been approached by Helheim in both games with peace agreements. In one of the games I am touching Helheim's border, in another game, I have no idea where Helheim is so I am thinking this has something to do with the Helheim victory formula

.
Btw, this is 3 different players playing Helheim the exact same way.
I did not mean for this to become a Helheim rant, but I am guessing if you followed this same strategy with Helheim in MP, you should be successful right out of the gate in your MP play. If three different people in games I am currently playing are using this exact same strategy, there must be something to it.
Another observation. I used to wonder why the race for the unique artifacts was so important, it seemed like you could focus on other things. Now I understand the real reason. At the end of the game, the stronger nations are pretty much on even grounds. If the players are of comparable skill level, the only advantage one player will have over the other is Unique artifacts and summons. That is probably why the race to grab up all the artifacts is so important beyond just having really cool items.