Spiked mines explode violently when they lose all their spikes.
~ BTD6 Official Description
Spiked Mines is the 4th upgrade of Path 1 for the Spike Factory in Bloons TD 6. It allows its depleted spike ball piles to create powerful explosions, dealing 10 damage each onto up to 40 bloons, alongside a powerful napalm that deals one damage per 2.0s for 6 seconds. The blast radius of the explosion is 19, around the size of the explosions from Bigger Bombs. Explosions deal double damage if the spiked mines automatically expire rather than if the spiked mines are fully depleted. Each spike also deals +6 damage versus Ceramics instead of +3, for 8 damage versus Ceramics.
The main power comes from the heavy explosives that spawn from emptied spiked mines. These deal 10 damage each, enough to shred through stronger bloons and deal a chunk of damage to blimps. The main use for the Spiked Mines in most games is to beat difficult pre-Round 81 bloon rush rounds with ease. Compared to other Spike Factory upgrades, it is surprisingly good at beating Regrow Bloons (with the exception of Regrow Blacks and Regrow Zebras), and it cleans up densely grouped bloons very effectively, unlike its previous upgrade Spiked Balls. In fact, Spiked Mines can be used as a pure offensive stockpiling tower with the 4-2-0 crosspath, although still better suited for tanking bloons as most Spike Factories are designed to do.
Use this if grouped bloons are a serious issue. Spiked Mines is effective at wiping out dense bloon rounds such as Rounds 63 and 78, and it can also be used to counter Regrow Bloons if the Regrows do not overmultiply.
Similarly to Ground Zero base bomb attacks, Spiked Mines explosions are highly potent at large-scale damage, but they heavily struggle against dense groups of Blacks or Zebras due to the explosion immunities of those bloon types.
It is usually better off using a 4-2-0 Spiked Mines over a 4-0-2 Spiked Mines in most situations. 4-2-0 offers a greater offensive potential, but 4-0-2 Spiked Mines can be used on certain maps where Spiked Balls armies would be unfavorable or to act as a cheaper substitute to Perma-Spike.
The only time where a 4-0-2 Spiked Mines truly matters is on maps with multi-lane intersections such as Rake and Sanctuary. It has seen some use on successful Ravine CHIMPS runs as a substitute for The Big One.
Compared to Spiked Balls armies, Spiked Mines is more cost-efficient at overall DPS on single-lane maps, although Spiked Mines has the disadvantage of no full discounts from Monkey Commerce.
Because the mine explosions can't damage DDTs without MIB or similar, Spiked Mines may struggle versus DDTs. Having Striker Jones Level 5+ helps counter this, but then again Spiked Mines isn't a reliable anti-DDT option whether its explosions can damage them or not.
Spiked Mines had been buffed overall throughout updates in this game. Substantial damage buffs for the explosions, added price reductions, an increased blast radius, and several Spiked Balls inherited buffs have made the Spiked Mines upgrade stronger in mid-game settings, more specifically versus mid-game grouped bloons.
During the 20's updates, Spiked Mines has consistently been buffed in order to compete cost-efficiency as a grouped damage Spike Factory versus the mid-and-late-game flexibility of Spiked Balls.
Spiked Mines costs less ($14,000 → $12,000).
Spiked Mines explosion deals more damage (4 → 5).
Spiked Mines explosion deals more damage (5 → 10).
Spiked Mines spikes now deal +1 damage to all bloon types.
[...] Along with this we made a couple small tweaks buffing what should be the 'strength areas' of a few of the more underperforming high tier Spike upgrades
~ Ninja Kiwi, referring to Spiked Mines, Carpet of Spikes, and Deadly Spikes
We quite liked how the lifespan changes for xx1 spikes went previously, though this still wasn't enough to make the path competitive and increasing this number further wouldn't have much of an impact since most earlier rounds aren't long enough. Spiked Balls strats have also felt too strong compared to higher tiers on top path, so touching on all of these issues slightly the base lifespan of spikes has been reduced, ceramic bonus increased on 4xx, and a new bonus added to 5xx. [...]
~ Ninja Kiwi, referring to both spike duration balance and Upper Path 1 balance
Base projectile lifespan reduced from 70s to 50s.
Spiked Mines spikes now deals extra Ceramic damage (+3 → +6).
Like a few other towers before it, the attack speed crosspath for Spike Factory has outshined the others. We have reworked the lower Spike Factory tiers to distribute this power more evenly while keeping high tier factories at a similar level of power.
~ Ninja Kiwi
Affected by Spike Factory crosspath speed changes.
Spiked Balls are used quite a lot, but we like their overall position right now so they have had only a slight bump up in price, along with a bigger decrease to the price of T4 Spiked Mines. [...]
~ Ninja Kiwi
Spiked Mines costs less ($12,000 → $11,000).
Pierce amounts for Spiked Balls and Mines fits their use cases too awkwardly due to super ceramics. Considering the power of Spiked Balls, their pierce has been reduced slightly to add value to the pierce focussed higher tier in addition to a price cut for Spiked Mines.
~ Ninja Kiwi
Spiked Mines spikes have less spikes (17 → 14)
Spiked Mines costs less ($11,000 → $9500)
All BTD6 Spiked Mines crosspaths
Spikes of Spiked Mines are slightly lighter than those of the previous upgrade, Spiked Balls.
Before Version 24.0, the Spiked Mines cost was the same as the first price buff in BTDB Mobile while the BTD6 Spiked Mines received its first price buff.
The napalm damage-over-time for Spiked Mines is the same as BTD5's Burny Stuff effect, which deals 1 damage per 2.0s for 6.0 seconds.
Spiked Mines received a buff to its spike damage versus Ceramics in Version 22.0 in order to give it more potential versus greater numbers of Spiked Balls, according to Ninja Kiwi's Version 22.0 patch notes.