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The obvious advice is to use an impaler to turn the blitzer into an artillery platform. At range 14 its possible to get some aimed shots in at a not-so-impressive-but-still-good-for-a-beast rat 7. The biggest thing to note is that you can boost a blitzers ranged attacks now, so you can hit at pow 13 on 3d6 which can take out most fleshy targets with relative ease. Grim doesn't do much for the Blitzer spell wise, attempting to use Marked for Death to easily tear through some stealth/high def-low arm infantry is a viable tactic, but Grim has to get within 8'' which is beyond his comfort zone. The blitzer will serve you well, but if you find yourself pushing it into melee too often dont be scurred to swap it out for a mauler.
...thnx man needed that help