Opinion: Designing the hand grenade

If you’ve ever fragged or been fragged by a frag then you’re probably familiar with the immediate and simple pleasures of the hand grenade. Very few of us, however, have spent time deeply considering the design of grenade mechanics and how different decisions creep their way up into the aesthetics of play. Their sheer and sudden power means they can reinforce or undermine a design. It is therefore crucial to understand the basic parameters of grenade design and the impact different design decisions relating to grenades can have on your game.

As with any design problem, the first thing to consider in grenade design is the aesthetic experience you hope to encourage. Do you want the frenetic adrenaline rush of run-and-gun play, driven by reflex and reaction? Or do you want a more deliberate, player-determined pacing that values positional play and more carefully considered tactical movement? If you are making Bulletstorm, it’s probably the former, while Rainbow Six may suggest the latter. Once you have a set of cohesive aesthetic goals, you can begin thinking about various mechanics and the dynamics they will likely promote.

An important first question is whether grenades will be a weapon you need to equip, or whether they will be assigned their own button. The need to equip grenades massively restricts their use, all but preventing them from being used in response to a sudden change of fortune. Play becomes highly consequential if the player has no quick way to reset the flow of an engagement.

Another critical question relates to the physical simulation and how effectively the player can predict trajectory, landing point and detonation point. Because grenades fly in an arc, HUD reticules can be inaccurate, and in-world reticules or trajectory indicators can feel clunky, forcing the player to make finicky manipulations. Conversely, without these indicators, players need time to internalise arcs and ranging for throws at different angles, and every throw is a ‘best guess’. You might need to consider designing and coding helpers that improve those guesses – especially as relates to ground friction. If a grenade lands short of an obvious cluster of targets, let it bounce and roll a bit farther. If it lands on target, stop it dead.

The more confidence the player has that he can use grenades effectively, the more likely he will be to keep using them, the better he will get, and the less you will need to rely on helpers. As with any such helpers, though, test them rigorously and disable them in competitive multiplayer modes.

Another thing to consider is whether you want grenades to be a weapon for killing, or a weapon for flushing enemies from cover. Making grenades that stick to, or explode on impact with, living targets makes for lethal direct attacks. If making these choices, you might also want to keep the radius small, and make AI less responsive to nearby grenades so that grenades typically only take out one enemy at a time, and don’t disrupt others. On the other hand, if you want grenades to be a tool that allows the player to reset the flow of a poorly trending combat, then larger radius, lower damage grenades that compel the AI to escape are a great tool.

How many grenades the player can carry at a time, and how frequently they are found in the world, are factors that determine how often they will be used, and affect all of the above considerations. Keep in mind that players tend to hoard rare resources; as the scarcity of a resource increases linearly, the tendency of the player to use the resource falls off exponentially. If you have obvious bosses, then powerful, rare grenades are probably smart. If you have lots of waves of fodder then weaker, ubiquitous grenades will likely better support your design.

Damage fall-off curves are intimately tied to your level design and can only be determined by endless tweaking in real game environments (not just test gyms!). Having long fall-off curves, and thus larger radii, can be computationally expensive, especially if you need to occlude damage in tight or cluttered environments. In general, low to moderate radii with higher damages will give you more freedom to tune, and are better for interior games, while larger radii with moderate damage blasts work better for exterior games, while also tending to work better with an AI that may have more freedom to move.

Whether or not to give players the ability to ‘cook’ grenades by holding on to them to deplete the timer before throwing is an important consideration for multiplayer. With practice, experienced players can become very skilled at cooking grenades to have them explode right next to their targets, leaving new players at a serious disadvantage and adding a barrier to entry. At the same time, the option to cook affords more highly intentional play.

These are just a handful of the dozens of factors that need to be considered in the design and implementation of grenades, but hopefully they will be a starting point for those setting out to design grenade mechanics for the first time, or for players with an interest in why superficially similar games can feel so different.