Crosspathing/Spike Factory

In Bloons TD 6, it is important to choose the best crosspathing for a specific tower in order to receive the best benefits out of that tower type. Towers have special roles to play for each stage of the game. The Spike Factory in its core is to produce and stockpile spikes to create a barrier that will prevent bloons from getting over it.

Introduction
The Spike Factory's main role is to stop bloons from reaching the exit. The main value of this tower comes from its stockpiling potential. It does so by producing spikes onto nearby track. Spike Factories produce spikes quite slowly, making them usually not suitable for direct offense. Normally, they should be placed at as back of the bloon track as possible to make the most amount of spikes possible before bloons reach their spikes, but some upgrades allow the Spike Factory to become suitable as a frontline offensive option.

Tier 2 and below



 * 0-0-0: Useful for tanking bloons on a certain lane. Multiple of them can be added nearby each exit to protect multiple lanes while not relying too much on spike placement RNG.
 * 1-0-0: Cheap but effective way to boost the amount of spikes produced per Spike Factory.
 * 0-1-0: Sometimes used in combination with Benjamin to potentially produce more spikes affected by Biohack.
 * 0-0-1: In rare case where extra range or extra spike lifespan may be necessary, this upgrade can be helpful in itself. Otherwise it's just a stepping stone for 0-0-2.
 * 2-0-0: The cheapest method to pop Camo-Lead Bloons with a Spike Factory. Normally more used as a stepping stone to Spiked Balls.
 * 0-2-0: It is mainly bought to use as stepping stone for 0-3-0 MOAB SHREDR, but it is worth crosspathing before then, unless under a strict budget.
 * 0-0-2: If specific spike dispersion from a single Spike Factory is better than adding a second 0-0-0 Spike Factory, this particular crosspath can be handy.
 * 1-1-0: More efficient than multiple 0-0-0 Spike Factories on single-lane maps. Should be enough to reliably tank early-game Camo Bloons, and a little bit for Camo rounds before Round 51.
 * 1-0-1: Normally a waste of money, but it can be somewhat useful on Apopalypse Mode. Generally worse than 0-1-1 at refreshing but better at stockpiling.
 * 0-1-1: Normally a waste of money, but it can be somewhat useful on Apopalypse Mode. Generally worse than 1-0-1 at stockpiling but better at refreshing.
 * 2-1-0: Similar to 1-1-0 except it pops Lead and Frozen. More efficient than buying a second 2-0-0 Spike Factory.
 * 2-2-0: Similar to 1-2-0 except it pops Lead and Frozen. A lot more cost-efficient than buying a second 2-0-0 Spike Factory. Can be used as a way to tank the Camo Leads on Round 59 on easier maps.
 * 1-2-0: Produces many spikes, and is the most efficient at simply spike count. This makes it the most efficient low-level Spike Factory option for maximizing effects of bloons affected by a damage vulnerability ("debuff"), excluding Spike Storms and Carpets of Spike.
 * 0-2-1: Normally a waste of money, but it can be somewhat useful on Apopalypse Mode.
 * 1-0-2: Combines the benefits of Smart Spikes and Bigger Stacks. Normally would be used with 1-0-3 Long Life Spikes or higher.
 * 2-0-2: It can be used to direct attention to and from Leads, but the targeting specifically onto Leads can be a bit of an issue.
 * 0-1-2: Mainly a stepping stone for 0-2-3 Long Life Spikes and its further upgrades, although 0-1-2 Spike Factory is somewhat stronger than 1-0-2 during the start of the round due to utilizing the start-of-round bonus better.
 * 0-2-2: Mainly a stepping stone for 0-2-3 Long Life Spikes and its further upgrades, as a 0-2-2 is generally quite weak compared to other crosspaths, especially the 1-0-0 Spike Factory. Is somewhat stronger at the start of the round due to the start-of-round bonus

Spiked Balls



 * 3-0-0: Spiked Balls does better than lower-tier Spike Factories at tanking bloons because it can skip layers by dealing extra damage to all bloons especially against Ceramics. Normally should go straight for Spiked Balls unless crosspathing a 1-0-0 Spike Factory is needed, specifically in combination with Path 2 upgrades in most cases. The overall value of Spiked Balls noticeably improves when given crosspaths, Path 2 for better refreshments and Path 3 for stockpiling specialty.
 * 3-1-0: Better for the faster production rate and therefore faster refreshment and stockpiling of the powerful spiked balls. Normally, it is not wise to stop at this upgrade, but if the budget refuses to let 3-2-0 be afforded, it's acceptable.
 * 3-2-0: Almost always the better crosspath for the maximum production rate and therefore faster refreshment and stockpiling of the powerful spiked balls.
 * 3-0-1: Spikes last twice as long and can be shot further, but only the first mentioned benefit truly matters here, as the nature of the Spike Factory is to stockpile not to actively make attacks onto bloons.
 * 3-0-2: Gives a brief start-of-round attack speed boost and allows for specific spike targeting. However, the amount of spikes produced from this brief boost is quite low in comparison to other upgrades. Unless on a tight budget or on a map where the specific spike targeting or start-off-round attack speed boost is necessary (e.g. on Workshop CHIMPS for Round 40), 3-0-2 is normally not the best crosspath option. However, this spiked ball factory can be used as a single spiked ball factory, to be insurance on short maps and allow for other 3-2-0 spiked ball factories to build up spikes, having a bit of synergy with the two crosspaths.

Spiked Mines



 * 4-0-0: It is a bad idea to leave Spiked Mines without crosspathing, as this wastes potential for benefiting for it to either attack much faster or to let it target specific areas of the bloon track.
 * 4-1-0: By the time Spiked Mines can be afforded, it should not be difficult to upgrade this further to 4-2-0. Try doing upgrading a 4-1-0 Spiked Mines as soon as possible.
 * 4-2-0: Almost always the better crosspath for the maximum production rate and therefore faster refreshment and stockpiling of the powerful spiked mines.
 * 4-0-1: Spikes last twice as long and can be shot further, but only the first mentioned benefit truly matters here, as the nature of the Spike Factory is to stockpile not to actively make attacks onto bloons.
 * 4-0-2: Gives a brief start-of-round attack speed boost and allows for specific spike targeting. However, the amount of spikes produced from this brief boost is quite low in comparison to other upgrades. The only time where this crosspath may matter is on a map with multiple paths such as Rake. In fact, 4-0-2 Spiked Mines has been used in some successful Ravine CHIMPS runs.

Super Mines



 * 5-0-0: There is no reason to leave it without a crosspath. It is extremely expensive, and much of its extreme high-damage value comes from crosspathing.
 * 5-1-0: See 5-2-0
 * 5-2-0: Almost certainly the better crosspath due to the fact that its explosions are huge already, and adding extra lifespan and a very insignificant start-of-round boost is severely overshadowed in comparison. The rate of expired explosions increases along with the increased rate of producing super mines.
 * 5-0-1: Useless because this locks out the potential for Path 2's bonus attack speed, and the longer lifespan does not have as much long-term value as 5-2-0, not to mention that the rate of producing giant explosions is slower and actually worsened by the longer lifespan.
 * 5-0-2: Equally useless because the start-of-round boost is too small to be noticeable, and the consistent extra attack speed is far superior. Since rounds are long anyway, the 5-2-0 most certainly produces more spikes than 5-0-2 even with its extra lifespan, and the rate of automatically producing huge explosions via expired super mines is decreased too.

MOAB SHREDR



 * 0-3-0: MOAB SHREDR is an interesting upgrade for the Spike Factory, as its huge MOAB-class damage rarely works effectively unless damaging only MOAB-class bloons. Because of this, placement at the back is less useful and heavy stockpiling isn't always the best approach for this specific upgrade. Path 1 is superior for a MOAB SHREDR because it tends to work better on the offensive than the defensive, mainly for chipping away at singular blimps. Otherwise, MOAB SHREDR is normally a stepping stone for Spike Storm.
 * 1-3-0: Better for the general higher numbers of spikes per pile.
 * 2-3-0: Can be used to damage DDTs. Comes with the 1-3-0 MOAB SHREDR benefits too.
 * 0-3-1: Spikes last twice as long and can be shot further, but only the first mentioned benefit truly matters here, as the nature of the Spike Factory is to stockpile not to actively make attacks onto bloons.
 * 0-3-2: Gives a brief start-of-round attack speed boost and allows for specific spike targeting.

Spike Storm



 * 0-4-0: This particular crosspath is normally used as a way to start its initial cooldown as soon as possible, and later on adding crosspaths to make the most of its ability. It can be upgraded to Path 1 for more spikes, or with Path 3 for some niche utility.
 * 1-4-0: Produces twice as many spikes during the ability. As of 27.0, it is now the preferred crosspath, and 2-4-0 can be bought to tackle DDTs.
 * 2-4-0: Can be used to counter DDTs. Rarely, it is used to counter the negative synergy with Icicle Impale, Absolute Zero, or other Ice Monkeys.
 * 0-4-1: Spikes dispensed from the Spike Storm ability last +50% longer, but this sole benefit is not significant alone.
 * 0-4-2: Worthy for handling rounds with singular blimps in a round, as well as for use on multi-lane alternating maps. Note that only the start-of-round effect affects the rate of spikes produced by the Spike Storm ability, giving it 4x attack speed in a narrow timeframe over consistently 2x spikes; activation at the start of a round is key. Targeting of only lanes that are guaranteed to be used on a certain round is nice to have, but the consistency from 1-4-0 is generally preferable except on maps with more than two alternating lanes and fewer than two wasteful lanes such as Muddy Puddles but not Bazaar, Chutes, Ravine, or Bloody Puddles.

Carpet of Spikes



 * 0-5-0: There is no point not crosspathing a Carpet of Spikes in a real game. It is much weaker without crosspathing. Use Path 1 for consistent extra pierce and lead-popping, or use Path 3 to utilize the special crosspathing benefits of +50% ability spike lifespan, potential 4x ability attack speed at start-of-round, and the targeting of guaranteed use lanes by the ability. Crosspath before upgrading to Carpet of Spikes for the best results, as Carpet of Spikes always produces an automatic spike storm once it is bought and the round is active.
 * 1-5-0: Produces twice as many spikes during the passive ability and for activated ability.
 * 2-5-0: Twice the spikes like 1-5-0, and also can naturally counter DDTs.
 * 0-5-1: Spikes dispensed from the Spike Storm ability last +50% longer, but this sole benefit is not significant alone. However, this means up to 3 layers of carpet can be active on the whole track at any one time instead of up to 2 layers. Opting for this upgrade misses out on getting twice the spikes per ability, which may or may not be the best trade-off.
 * 0-5-2: Activating the ability at the start of the round produces spikes at 4x the rate, making it produce 2x more spikes more compared to 1-5-0. In addition, it targets only lanes that are guaranteed to be used on a certain round. It is possible to get 0-4-2 and then quickly upgrade to 0-5-2 to instantly utilize the start-of-round boost, but only if bought while the round was starting. Without using these niches, consistent damage bonus of 1-5-0 is far better than the specialized targeting of guaranteed lanes.

Long Life Spikes



 * 0-0-3: If attempting to go straight for Perma-Spike, it is okay not to crosspath Long Life Spikes. Crosspathing it is more recommended, however, as its stockpiling potential can make mid-game a good chunk easier, especially in combination with Alch buff.
 * 1-0-3: Spikes have double the pierce, which makes it stockpile twice as many spikes. It is better than any Path 2 crosspath Long Life Spikes at stockpiling but worse at both refreshment and utilizing the start-of-round attack speed boost. It also isn't as good of a synergy with Alch buff compared to 0-2-3.
 * 2-0-3: Exactly like 1-0-3 except pops Frozen and Lead. It does not require an Alch buff to function at popping any type of bloon, but adding Alch buff is still a good idea.
 * 0-1-3: Better for the faster production rate and therefore faster refreshment and stockpiling of the long-lasting spikes. It is better than 1-0-3 at refreshment and utilizing the start-of-round attack speed boost but worse at stockpiling.
 * 0-2-3: Usually the much better crosspath due to synergizing much more with Alchemist.

Deadly Spikes



 * 0-0-4: If attempting to go straight for Perma-Spike, it is okay not to crosspath Deadly Spikes. Crosspathing it is more recommended, however, as its stockpiling potential can make mid-game a good chunk easier, especially in combination with Alch buff.
 * 1-0-4: Spikes have double the pierce, which makes it stockpile twice as many spikes. It is better than any Path 2 crosspath Long Life Spikes at stockpiling but worse at both refreshment and utilizing the start-of-round attack speed boost. It also isn't as good of a synergy with Alch buff compared to 0-2-4.
 * 2-0-4: Exactly like 1-0-4 except pops Frozen and Lead. It does not require an Alch buff to function at popping any type of bloon, but adding Alch buff is still a good idea.
 * 0-1-4: Better for the faster production rate and therefore faster refreshment and stockpiling of the long-lasting spikes. It is better than 1-0-4 at refreshment and utilizing the start-of-round attack speed boost but worse at stockpiling.
 * 0-2-4: Usually the much better crosspath due to synergizing much more with Alchemist.

Perma-Spike



 * 0-0-5: There is no reason to leave it without a crosspath, unless going straight for this upgrade.
 * 1-0-5: Unlike most Spike Factory upgrades, adding Bigger Stacks increases the pierce of Perma-Spike spike piles by +80%. It very slightly outweighs spike production rate compared to 0-2-5, but synergizes less with Alch buff and refreshes much slower.
 * 2-0-5: Exactly like 1-0-5 except pops Frozen and Lead. It does not require an Alch buff to function at popping any type of bloon, but adding Alch buff is still a good idea. 0-2-5 Perma-Spike is still superior to a 2-0-5 Perma-Spike, assuming Alch buff is available.
 * 0-1-5: Better than 1-0-5 at refreshment and synergizing with Alchemist and the start-of-round boost, but worse at stockpiling. Still, go for 0-2-5 Perma-Spike and don't stop at 0-1-5.
 * 0-2-5: Usually the much better crosspath due to synergizing much more with Alchemist. It gives +79% more spikes overall and refreshes much faster.