Grenades, and explosives in general, are tricky to write rules for in most d20-based ttRPGs. If a grenade isn’t effective enough, it feels more like a firecracker than a deadly weapon of war. If it’s too effective, it can end encounters so quickly it’s no fun for the players, or accidentally wipe out PCs in undramatic ways.

When grenades show up in action/adventure fiction, they tend to act less as damaging devices than plot devices that force people to seek cover. The threat of them is generally represented not by them killing main characters, but by forcing characters to take them seriously and possible shake off effects of shock and awe.

Example: Starfinder Revised Grenades

So, let’s try to model that behavior, specifically for Starfinder. Within that game, grenades are pretty expensive consumables anyway, so a power-up shouldn’t break the game even if it makes grenades more affective and appealing. That said, if these seem too powerful, you can limit these rules to actual purchased consumables, rather than spells and class features that allow characters to create or emulate grenades without a credit or OPB cost.

Grenades

Grenades are dangerous, deadly military explosives that everyone must take seriously as a threat, no matter how tough or resilient they are. While savvy and active combatants know to duck for cover and shake themselves free of the shock of battlefield explosions, doing so comes at a cost.

When you fail a saving throw against a grenade that has an item level no lower than your character level/CR -2 that deals damage (as opposed to, for example, smoke grenades), you must either expend a Resolve Point or be staggered on your next turn. This represents the need to duck, take cover, and shake yourself back to focus after narrowly avoiding more serious injury.

Helpless characters that fail a save against such a grenade treat the attack as a coup de grace against them. As a full round action a character can make an Engineering check (DC 15 + 1.5x grenade item level) to wedge a grenade into an adjacent stationary structure or unattended object, causing it to do max damage and have only half its normal explode radius. On a failed check, the grenade explodes in the character’s hands, and they take max damage.

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