Spikes last much longer and can carry over one round.
~ Upgrade description in BTD6.
Long Life Spikes is the 3rd upgrade of Path 3 for the Spike Factory in BTD6. The spikes produced by the Spike Factory can pop the same amount of bloons as the base form (which is 5, or 10 with Bigger Stacks, +1 if the "One More Spike" Monkey Knowledge Point is active). However, the spike piles are now modified into blue caltrop-like spike piles. These spikes can last much longer than the other spikes produced by the Spike Factory. They can last up to two rounds or 140 seconds, whichever comes sooner.
Long Life Spikes is a rather expensive but versatile upgrade once purchased. By allowing each spike pile to last between rounds, it is possible to stall rounds in order to stockpile many spike piles that can become carried over to the following round. Generally speaking, when attempting to pursue towards maximizing the potential of Long Life Spikes, it is worth purchasing Faster Production and Even Faster Production alongside to allow maximized net popping power stockpiles. Similar to the much more powerful Perma-Spike, Long Life Spikes is a deadly force when combined with Berserker Brew/Stronger Stimulant and Jungle Drums. Similar strategies can be used for the succeeding upgrade Deadly Spikes.
Always purchase this upgrade on single-entry-single-exit maps near the end of the track. Then spikes won't be used up immediately, allowing spike stockpiling to slowly make the tower more and more valuable.
Path 2 upgrades will add +79% extra pops with a fast refresh, while Path 1 upgrades will add +100% extra pops with a slow refresh and allows Lead-popping. While 2-0-3 is better at overall spike production, 0-2-3 is much faster and synergizes much better when paired with Alch buffs.
Avoid leaving the game, as the stockpiled spikes do not carry over between saves.
It has been proven that Long Life Spikes does NOT decrease spike amount when purchasing Bigger Stacks. Click for the link.
One 0-2-3 Spike Factory costs $4690 on Hard Difficulty. Although it is not as important as it was prior to the Overclock rework, a 0-2-3 Spike Factory can still be useful early mid-game.
The spikes produced by Spike Factories with this upgrade look somewhat similar to the Caltrops that Ninja Monkeys use.
This spike factory appearance mostly resembles the Bloons Tower Defense 5's MOAB-SHREDR upgrade.
Prior to the rework of Overclock's ability, double-discounting the whole 0-2-3 Spike Factory with two Monkey Commerces was used to make an Overclock on Perma-Spike last 15 seconds longer. This is because this discounting would bring down the total cost of the 0-2-3 Spike Factory to ~$3752, thus bringing down the total cost of Perma-Spike to be ~$39932, barely below the threshold for Overclock's duration penalty for $40,000+ towers.
Now, Perma-Spike overclocks will only last 30 seconds.