I've had to have a bit of a think about the Daemon Prince, I definitely like the new incarnation, although the passing of Lash will be looked on with sadness/joy depending upon your perspective. I'm going to go the for controversial option here and say that I'm saddened by its passing. I never played Lash Chaos, so I'm not saddened by it because I now can't use another cheesy combo. The reason I'm saddened is probably down to a sense of nostalgia. About a year after I first got into 40k my gaming buddy started using a dual Lash Prince, Tri defiler list.
The first time I played against that with my Footdar I was tabled and only managed to kill a single Thousand Son in the process. I didn't mind him playing the list, because during this period my game really started to improve, and although it took me 2 years to beat the list, I came out of that a much better player than I had started as. That's probably expected due to my increase in experience but I believe that playing against a hard list like that drove me to want to improve my play as much as I possibly could. Plus, Lash was quite common in my community and although I played against it a lot I have won every game against a Lash list that I've played since I first beat it at the end of 2010, because I'd played it so often that I knew exactly how to deal with it.
But anyway, that's past, onto the present. The current Daemon Prince has one heck of a beasty statline. I'm actually thinking of bringing back the Arena once I've finished analysing the Chaos Codex and watching a bear DP fight the Avatar of Khaine. It's 10pts cheaper than an Avatar though, but anyway. How are you going to kit this guy out?
Well for a start you have to take a Mark, so which one to take? Well, starting off generically, each Mark gives you hatred against Daemons of the polarized God, I'm not going to state outright which hates which but Lexicanum will tell you. But, other than that, they all come with their own nifty rules. Khorne gives you furious charge, Nurgle gives you shrouded and slow and purposeful. Slaanesh comes with quite a few, +3” to your run, fleet and rending. But my favourite by far is Tzeentch, which allows you to re-roll all saving through results of 1, being familiar with this through my Space Wolves I'll come on to how nasty this can be in a minute. All of the Marks cost the same, with the exception of Slaanesh which is 5pts cheaper and all 5 give you access to Mark associated psychic powers, with the exception of Khorne of course.
Now, moving onto individual upgrades. You can give him Wings, a good decision. Why not make your 200+pt Monstrous Creature flying, they're nasty. The one I probably have more to say about however is the humble upgrade of power armour. For 20pts I really think that this is mandatory. Especially considering the Daemon Princes Toughness of 5, as otherwise I can drop a Manticore missile on you and 2/3rds of the time that is going to result in a dead Daemon. So, give him a 3+ save to mitigate that. Now, normally I still wouldn't like the risk for such an expensive model, but remember, you have a Mark of Tzeentch, and now, half of the saves that you fail are going to allow you a re-roll, that's pretty nice.
You can also give your Daemon Prince psychic mastery levels, so he doesn't have to take any psychic powers at all, for the same cost as the Sorcerer has to pay per level. I probably wouldn't go with this, I'd like to keep my DP as inexpensive as possible, especially when I would be paying 25pts for something that is essentially random. If you're going for the biggest beatstick that you can find. Sure why not? But then you'll also want to dip into the Chaos Rewards, etc, which I'll come onto now.
I probably wouldn't take the rewards. I've heard about taking the Axe of Blind Fury but then I'm not getting Mark of Tzeentch, plus I'm a WS9 S6 Monstrous Creature with 5 attacks anyway, and this isn't something that I'd really like to go overkill on. So essentially, this is how I'd set up a Daemon Prince.
Daemon Prince: 220pts
-Mark of Tzeentch
And that's already pretty expensive.766 words. Cutting down.