Dark Vengeance
Mission One: Rampage

This mission is more about control than overt destruction. The mission overview and battle tactics paragraph at the end of the mission notes cover this elegantly. One main feature of this mission is that you have a good idea about how your opponent is going to act. This means that you can plan your actions a few steps ahead.

With this in mind, let's have a look at how we can use the Helbrute's actions in our favour.

The Movement Phase

The Helbrute will move, and later shoot at the nearest unit. As the mission tactic section suggest you are advised to make sure that this is your cheapest, most expendable unit. For the Chaos army this will be the Cultists ( please note that in all real word cults and religions this is the case too. The leadership care about the Cultists right up to the point where they are threatened, and then the Cultists become expendable).
As the Chosen weapons are the best tools to take a wound/ hull point off the Helbrute, then you will want to draw the Helbrute away from the Chosen so that they can get a good shot at the Helbrute's back where the armour is thinner. However you should note that several of the Chosen's weapons have a 12" range. Using these weapons will place you within assault range of the Helbrute.
Another option will be to have the Cultists with the heavy stubber behind the Helbrute. This has 3 shots a turn with a 36" range and will glance the Helbrute's armour on a 6. As half of the shots are expected to miss you are in no fear of killing the Helbrute.

The Shooting Phase

The Helbrute will always shoot at the nearest unit. This should be the one that it was just moving towards, so probably the Cultists. The size of the playing area means that the Helbrute will always be in range of the bait (Cultists?) in the first round.
If you arrange the Cultists carefully you can minimize the casualties received from the Helbrute's flamer.

The Helbrute's Assault phase

The Helbrute will be rolling 2D6 (average of 7) for the assault movement distance. On a 2' ( 60cm) playing area that will mean that it is very likely that the Helbrute will get into assault.
When the Helbrute has finished dishing out the punishment you probably want to use the ' our weapons are useless ' rule ( Page 26) to fall back leaving the Helbrute free from combat letting the other units shoot at the un engaged target.

How to make the mission easier

Although this is the first mission in the book, it is not an easy one to complete. If you want to make the mission easier to start off with try the mission on a larger playing area of 3 foot by 3 foot. This will give your troops more space to maneuver in and a better chance of staying out of assault range from the Helbrute.