The new Tyranid codex got a number of new units; some of them, like the Trygon and Hive Guard, got a lot of attention. Others, like the Tyrannofex, were not so well-regarded. Amongst those that got a lot of negative attention was the Harpy, a strange flying gun-beast with a mix of shooting and melee abilities that puts it in a very unusual place. However, like many units in the codex, the Harpy is actually much better than most people give it credit for and indeed has a number of unique features that make it a standout at certain roles.
The basics of the Harpy are fairly simple. It comes with a twin-linked main gun- a Stranglethorn base, or Heavy Venom Cannon if you pay a token number of points. It also gets the usual secondary gun, which will always be Cluster Spines, as with every other MC. It gets jump infantry movement and a statline that is above-average for most units but a bit short for an MC- 5s across the board, mostly, but with BS/WS 3 and only two attacks. Scything Talons round out its loadout of normal gear.
It also has several unique features, of varying usefulness. Once per game when it flies over a unit it can "bomb" them, dropping d3 Spore Mines on them. This will almost never be relevant for several reasons; as we will see later, the Harpy's best defense is staying at range, so you often won't be close enough to do it. Even when you have the chance to do so, it is risky- due to extremely poor planning, the Mines' AP4 is enough to punch through its armor save, so you have a not-unreasonable chance of doing one or more wounds to yourself. As a result, even when you have the chance to use it, you often will not.
Its other abilities are more helpful and provide an interesting contrast to its primary shooting role, as they support a melee engagement theme. It is one of the three units with Offensive Grenades in the codex and on the turn it charges a unit, the target's Initiative value is halved. This will rarely be much benefit to the Harpy itself, as I5 is enough to strike before most anything you would be willing to charge, but it can be tremendously helpful when you are multi-charging.
So what do we get out of all of this? Well, first off, the Harpy is for shooting, specifically for shooting tanks. It's TL HVC is one of the most accurate anti-tank guns in the codex and it comes with better range (36") and mobility (12" move) than anything else we can get. This is especially notable against the various Fast Skimmers and Tanks out there that can otherwise maneuver to deny us shots with Hive Guard due to their limited range. Since it is in the FA slot, it also is one of the few such units that does not compete directly with Hive Guard, which is a further benefit. In a pinch, however, it can put out fairly significant anti-infantry fire (small blast and large blast), as with most of our MCs.
The Harpy has a big weakness, however: fragility. T5 means it will take about twice as many Bolter rounds as other MCs will, and 4+ save only makes this more of a problem. Worse yet, Autocannons, Scatter Lasers, and Heavy Bolters, traditionally guns that annoy our other MCs can be fairly devastating to the Harpy. To use it effectively, you absolutely must use its mobility and range to limit what the enemy can engage it with and keep to cover. Depending on how you built the model, this may be more or less problematic. However, in some other ways the Harpy is actually quite resilient; it has the full four wounds like other MCs do and, against Missiles, Meltaguns, Lascannons, Lances, etc, it can take just as much damage as anything else. T5 does mean that you can be killed instantly by S10 attacks, but realistically there are only two of these in the game: Railguns and Manticores. Against Tau you should probably use it to play "hide and seek," flanking their forces and making him maneuver and split fire to deal with the Harpy. The Manticore is a much easier target- just aim your shots and suppress it each turn, as you probably don't want to let it be active anyways.
Speaking of suppression, a lot of people complain that the Heavy Venom Cannon is a bad gun; yes, the -1 on the damage table is a disadvantage, but you can live with it. As with many other armies, your purpose with the Harpy and its gun is not to kill the enemy outright, but to simply keep them from doing anything while the rest of your army advances and does its job. If its target is still alive by the time you get close to is, you can simply charge and kill it, but for the most part a tank that isn't shooting is a tank that might as well be dead anyways.
The Harpy's secondary role at meleeing can also be a major boon in some circumstances- although it is a fairly poor combatant itself, with WS3 and only two attacks, it is still an MC and thus cuts through saves quite effectively, and S5 will consistently wound most targets. More importantly, it can be a key portion of a multicharge into a dangerous enemy, allowing your Warriors, Termagants, etc to get a guaranteed first strike on Marines or the various Eldar. Against enemies that lack a Power Fist or significant numbers of attacks it can also be useful as a delaying tactic- grenades and T5 allow it to assault places that might otherwise be inconvenient and jump infantry status lets it go where other units simply might not be able to reach. Oftentimes a Harpy will be able to lock a unit in CC for the one or two turns that you need to bring something stronger to bear, or to finish off the last remnants of a squad that is still causing you problems.
So what does all of this sum into? The Harpy is a good choice for armies that want to bring anti-tank shots beyond their allotment of Hive Guard and/or are worried about problems with fast vehicles... in some circumstances. My experience has been that in larger games the chances of facing down S10 or massed AP4 simply grow too high; 2000pts is probably the cutoff, and even 1850 is stretching it somewhat. 1750 is probably a more comfortable number and down to 1500 it is quite useful. Below 1500 you simply don't have the points to take it in addition to your HG, so it's a non issue. This leaves us with a fairly small window in which it is useful, but a window that sees play none the less.
