Grenade Mod

Grenade Mods are useful pieces that modify the properties of your Protean Grenades by increasing their damage, changing their functionality, and/or adding elemental properties. They are named by their elemental property followed by their type, such as Explosive MIRV or Incendiary Rain. When getting rid of what appears to be duplicate mods, be aware that they may have significantly different damage ratings from each other, even if they have the same name and color. Grenade mods are dropped by enemies, found in skag piles and chests, and can be given as quest rewards. They can also be bought as "Item of the day" at Ammo vendors

Contact
Contact grenades detonate immediately upon contact with an enemy when first thrown. They do not function as proximity mines while on the ground, if they do not impact an enemy they will explode like a regular grenade a short while later. They are useful for characters oriented towards melee, since the closer a target is, the easier it is to hit them with a contact grenade.

Rubberized
Rubberized grenades behave as a rubber bouncing ball when thrown, continuing to bounce along the ground or off any other surface until they explode. While these may appear useful for distant enemies, as it takes longer for a rubberized grenade to go off than most grenades, they are likely to take odd bounces and not reach them. However, rubberized grenades also explode both on contact and on close proximity to enemies, which can help to counteract this, especially indoors. In cramped areas such as the rooms and corridors of Sledge's Safehouse, Rubberized Grenades are all but impossible for the enemy to avoid. Simply throw a grenade in the room, shut the door, and wait.
 * There is a glitch in which you throw a rubberized grenade just right at a Vendor to get it stuck on the Vendor. It will twirl as though hitting an object or just flying through the air, and will produce sparks from hitting the machine, then explode after a short time.

MIRV
MIRV grenades are highly effective cluster bombs and explode at a preset time after they are thrown. When MIRV grenades explode, they throw out several more grenades, which subsequently explode. MIRV grenades are highly effective against groups of closely concentrated enemies, and become especially effective when they start boasting an Elemental effect, particularly Shock and Incendiary types.

You can use MIRV grenades to cover a wide area of effect by using them as an 'airburst' grenade; MIRV explode about three seconds after they are thrown, whether they hit the ground or not, so you can throw the grenade higher to make it explode in the air and spread the cluster bombs farther.

More info at Wikipedia's article on MIRV.

Bouncing Betty
Bouncing Betty grenades are standard grenades that "jump" into the air before exploding and throwing bomblets straight out from the central blast. These are similar to MIRVs, but because they go up in the air before exploding, they can hit foes hiding behind objects which MIRVs cannot. Between BBs and MIRVs, choose the one with the higher damage rating and sell off the other. As noted in Wikipedia, "Bouncing Betty" was originally the nickname for a German land mine. Bouncing Betties also have bugs in that if they land in certain spots, the grenade will not explode and simply disappear. Bouncing Betties can also be caught in small nooks and crannies which will effectively eliminate their wide spread because the nearby geometry catches the explosion.

Transfusion
Company: Anshin

Transfusion grenades are essentially vampiric grenades. They explode into a storm of white trails, which seek out enemies and damage them, turn red and return to you. When the red trails hit you, they heal you for the damage dealt. The explosion itself deals no damage, and the trails will travel an impressive range to seek out enemies. Transfusion grenades have no elemental property. If you are already at full health, it is normally better to switch to a grenade mod which will deal more damage, but keep the Transfusion grenade mod until you do need it.

Note that transfusion mod grenades will actually heal the closest friendly unit, not just you. If you throw the grenade from far away and your teammates are closer, they will be healed. Also if there's a Claptrap unit around, it may also be "healed"...and you won't!

Transfusion grenades don't work on Mothrakk - the white trails just head off in their default directions when you throw them up into the air.

Also if you are a soldier, Transfusion can also heal your scorpio turret.

For some reason, if a Transfusion Grenade's blast radius is near a propane tank, it will detonate the tank and heal the player to full heath even if no enemies are present.

Sticky
Sticky grenades do not bounce, instead sticking to whatever they impact with, be it a floor, wall, or an enemy, making it easier to aim. After a few seconds, the grenade explodes. Other grenades may bounce along and explode past the opponents. Sticking a grenade to an enemy's weak point, inside a skag's mouth for example, can give the grenade a high chance to cause critical damage. However, a multi-explosion grenade is usually more effective.

Rain
Company: Atlas

Rain grenades launch themselves into the air then explode, the resulting explosion rains down in a cone shape around the original grenade affecting all targets in the area. When choosing between MIRV, Bouncing Betty, and Rain, the deciding factor will normally be the damage rating each has; keep the strongest and sell off (or dump to make room) the rest. Rain grenades have a unique effect for each element : fire grenades pop up and launch a flamethrower-like blast downwards, corrosive pop up and causes a waterfall of acid to rain down, shock causes thunder bolts to drop from the grenade, explosive causes smaller bombs to drop onto enemies. As with Bouncing Betties, Rain grenades will sometimes bug, vanishing rather than popping up and detonating.

Longbow
Manufacturer: Hyperion

Longbow grenades teleport (not instantly, but travels very fast) to the point you are aiming at and explode a few seconds later. This makes them very accurate, since you do not need to arc them, although if they strike a wall or ceiling, they will obey physics for a short time rather than exploding at the exact point of impact. They will teleport directly to the first object that would stop a normal bullet including walls, cover, and enemies themselves. (Note that doors covering spawn points often do not count, even if they look solid, such as the roll-up doors in Old Haven; the grenade may go through the "barrier" and explode ineffectually.) It is best to aim for the ground at the enemy's feet or at walls/objects immediately behind the enemy. Enemies behind cover or with no other objects nearby can be difficult to damage with Longbows since the grenade must be aimed at and hit the enemy itself, and even if you do strike the enemy, the grenade might bounce down in front of their cover before exploding. For amazing accuracy, use a sniper rifle or any weapon with a decent scope to pinpoint your throw. When hiding behind cover occasionally Longbow grenades will impact invisible edges of the cover near the player's left side. Be careful if throwing Longbow grenades with cover to your left.

They are also excellent at flushing human opponents from cover; if a Longbow grenade is bounced off a wall behind a group of Crimson Lance(for example), the resulting disarray can be very damaging to an enemy position even if they all sucessfully avoid the blast, and if nothing else they are likely to stop shooting while they scatter, easing the pressure on players.

In addition to direct combat, the combination of high accuracy and relatively low damage makes Longbow grenades an excellent choice for grenade jumping. Depending on the map, this can be far more useful than using them to damage enemies.

Proximity Mine
Proximity mines can be thrown and will wait (a few minutes) to explode until an enemy comes near. "Smarter" enemies will avoid triggering the mine, allowing for the player to separate enemies from each other to make them easier to deal with, block off a chokepoint, or otherwise provide general area denial. Proximity mines cannot be triggered by other explosions or allies walking over them. They can also be attached to just about any surface; and will detonate a few minutes after being set if not triggered by an enemy. Again, since smarter enemies will avoid them, this mod is less valuable as an offensive weapon. It may be useful as a defensive weapon when being chased, where the enemy will be harder to target with a standard grenade.

Glitches

 * As stated before, certain grenades such as longbows or bouncing betties, may disappear after hitting something instead of detonating
 * There is a glitch with the longbow grenade where after hitting an uneven surface (i.e an NPC or a sloped ground) the grenade may strangely duplicate (physically, not visually, as the damage actually doubles)