Lightning Bolt is the second upgrade on path 1 for the Monkey Apprentice in Bloons TD 5. It costs $1020 on Easy, $1200 on Medium, $1295 on Hard, and $1440 on Impoppable. This upgrade has the most popping power of all the cheap upgrades of the Monkey Apprentice, with a popping power of up to 25 bloons. The lightning bolt can also go out of the range of the Monkey Apprentice. It is a commonly used upgrade during the earlier rounds for its popping capabilities and if upgraded to Monkey Sense, it can take care of weak Camo Bloons, but stronger Camo Bloons (e.g. Camo Ceramics, Regrow Camos) would require far more popping power. Do note that the lighning bolt only pops one layer of bloon at most.
On the update where the track Jungle was released, this upgrade was buffed; allowing the bolt to reach farther and as a visual effect, most of the parts are enlarged for added realism. Also, the price was reduced.
This upgrade was nerfed two times, and buffed two times: in August 2, 2012 the cost (in Medium mode) was increased from $800 to $1200; in November 15, 2012 the cost was increased from $1200 to $1300; in June 13, 2013 the cost was decreased from $1300 to $1250; in September 27, 2013 the cost was reverted back from $1250 to the old $1200.
Previously, with the upgrade Dragon's Breath, the Disciple of Fire was unable to fire magical and lightning bolts. This was fixed in an update, but then the cost of Dragon's Breath was increased from $3500 to $4200. It can fire lightning, but not magic bolts.
It appears as if the lightning bolt is fired from the Apprentice's head/hat, not from her hands like in the artwork.
Lightning Bolt are considered quite noisy if exposed to large volume, especially when using headphones.
It may also cause lag as Lightning Bolts can try to make details that takes time to create.
In the mobile version, lightning bolts does not cause any additional sound.