The cryo grenade deals only one point of damage to targets, but will freeze them solid for 3 seconds. Take that time to get a few easy shots on the foes with a more powerful weapon. Or, use it to freeze a non-player character in possession of a unique weapon, then take it from them while they're frozen.
Thrown grenades are affected by physics; they may bounce or roll unexpectedly if not thrown carefully. However, in game physics can also be used to your advantage; such as throwing grenades through doorways or bouncing them around corners to attack enemies who cannot see you.
Grenades can be targeted in V.A.T.S. and can thus be shot out of the air. Shooting them whilst they are still held by the enemy can detonate them as well. Grenades can be thrown point-blank in V.A.T.S due to the sharply reduced damage taken.
A grenade that has been thrown toward you will show up on your HUD as a red arrow denoting its direction relative to you. Move in the opposite direction as quickly as possible to escape the blast radius.
Holding the fire button down for a longer period of time will increase the strength of the throw. Grenades can be thrown for longer distances than normal through successful V.A.T.S. hits. Grenades cannot be cooked to detonate earlier.
It is also possible to plant a live grenade on a non-player character by passing one from your inventory to the non-player character's inventory via pickpocketing.
These grenades can be obtained from Elliot Tercorien after releasing him from stasis and going through the cryo lab with him. He will pick up some cryogenic parts in the area where Beckett and Daniels are frozen which enables him to start making the grenades upon return to the engineering core. He will give you 3 cryo grenades and 3 cryo mines after you wait an hour for him to make them. After that must wait another 3 hours for him to make 2 more each time you ask. Elliot will not be able to make any more cryo grenades or cryo mines after he leaves the engineering core during the quest "This Galaxy Ain't Big Enough...".
The cryo grenade was originally a weapon cut from the final version of Fallout 3 for an unknown reason. It does not exist in the final version of the game, nor does it exist as an unused item in the G.E.C.K. editor. However, the mesh and texture are contained within Fallout 3's BSA files, these files however were not used and new meshes and textures were made to replace them in Mothership Zeta. Another cryo weapon, the Cryolator, exists only as a mesh and textures in Fallout 3's BSA files.
Reverse Pick-Pocketing a cryo grenade or a cryo mine, then backing away from the non-player character will freeze the non-player character, while stunned you can pickpocket them at will.