Hive Guard
The Hive Guard are presumably related to the Tyrant Guard, as they look somewhat similar and have similar names. The Hive Guard are shooty, and quite powerfully so; they are equipped with what essentially are biological railguns that function as an S8 AP4 Storm Bolter that ignores cover and line of sight. As such, they're quite good at popping enemy transports, and can be used against most vehicles, if you can get them into the rear armor arc. With T6, 4+ saves, and 2 wounds they're also reasonably durable, having a toughness value too high to be instagibbed by high strength weapons, an okay armor save (though one that's ignored depressingly frequently, especially in a meta that loves it's mid-strength shooting), and a good toughness value.
They are the fucking bane of Rhinos of Fury.
Seventh Edition
Hive Guard in seventh edition are quite the useful creatures. While their BS was dropped to 3, the Impaler Cannon (which they start with) now ignores line of sight AND cover. This means that vehicles that rely on jinking need to be extra careful and the amount of dakka a brood of these suckers can put out from a completely safe location, such as behind a BLOS wall, creates a zone that your opponent's lighter vehicles need to be wary of. Another "advantage" they have is the overall nerfing of Zoanthropes, making the brains much less of an auto-include and freeing up not only elites slots but requiring more reliable anti-tank. They do come with downsides, however. Their gun only shoots as far as a bolter, they have an average leadership, and their shock-cannon "upgrade" is complete trash. They are far more durable than they seem and can even win the odd assault if they aren't fighting dedicated assault units, but every turn they aren't glancing things is a turn they are being useless. If static defense is untenable for the mission, they need to keep advancing under the cover of a synapse creature. Luckily their complete lack of caring about LoS means that with creative movement your enemy should pretty much never be able to shoot them.
Upgrades
- Shockcannon: The only weapon upgrade hive guard have, the shockcannon pumps out a small blast with the haywire special rule. It's strong enough to do okay against infantry but it's hampered by its extremely depressingly short range of 18". The real icing on the cake? It loses the awesome ignores cover ignores LoS rules the Impaler has. And it costs 5 more points. MAYBE if you throw them in a Tyrannocyte and you know your opponent loves spamming land raiders. Avoid.
- Adrenal Glands/Toxin Sacks: Why? Your hive guard shouldn't be in assault. Perhaps adrenals if you REALLY want that fleet to get closer faster. If you ARE crazy enough to take adrenals on them, don't forget to paint them red.