Elemental Gems: What is the exact boost?
Tested with a Jolly 252 attack 31 IV lv. 50 Houndoom's Crunch vs. 29/31/31/2/31/31 lv. 50 Metagross with 252 HP, 252 attack, 6 defense.
Normal damage range: 42-52 HP
First 10 tests with Houndoom holding Dark Jewel vs. Metagross
69 HP lost
64 HP lost
66 HP lost
66 HP lost
67 HP lost
69 HP lost
70 HP lost
76 HP lost
66 HP lost
70 HP lost
This leads me to believe the multiplier is 1.5x, since 1.5x the normal damage range would be 63-78 HP. Even though I didn't get the absolute minimum or maximum values in the test, I got enough of a range to know it's between 1.4x and 1.6x.
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Bulb: Does it grant a (one-time) immunity to Electric moves, in addition to raising SpAttk? Does it raise SpAttk every time the Pokemon is hit by an electric move? Does it work with a Pokemon with Volt Absorb?
Bulb does not grant an immunity to electric moves, and once it's used, it disappears.
Volt Absorb activates before Bulb does, making it have no effect.