Crosspathing/Monkey Ace

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 Monkey Ace in its core is to fly around in the air at fixed flight paths.

Introduction
Monkey Ace is a unique tower that flies circles in the air by default, it shoots 8 darts at equal angles in a circular fashion that has a ton of pierce for a base tower. Because of this, it has a really big tendency to miss bloons, especially fast ones. Crosspathing with Monkey Ace comes down to whether or not the player wants the power of the Monkey Ace to come from its main attacks or come from a separate attack. Path 1 focuses on alleviating the Ace's main weakness by increasing the power and number of Dart's it shoots, and attack speed (like Top path Ninja Monkey) with upgrades like Lots more Darts and Operation: Dart Storm. Path 2 centers around creating high damaging explosives and dropping them onto the track with upgrades like Exploding Pineapple and Ground Zero. Path 3 also focused on alleviating Monkey Ace's weakness by allowing the dart to home in on bloons with Neva-Miss Targeting and eventually adding more DPS with Spectre and Flying Fortress. Crosspathing is very simple for the Monkey Ace: Unless going Bomber Ace, always ignore path 2.

Tier 2 and below



 * 0-0-0: Simple as an option for thinning out early-game waves while saving up for the Monkey Ace's upgrades. Pair a 0-0-0 Ace with reliable defense options, as a 0-0-0 Ace is easily prone to leaks.
 * 1-0-0: Increases the attack speed of the Monkey Ace.
 * 0-1-0: Drops a pineapple that explodes after three seconds. Due to how long it takes to explodes, its very common for the pineapple to miss its target and not even be on the track because the Monkey Ace can go off track, relative to its position on the ground. Its main use case is for a little extra grouped damage at a low cost.
 * 0-0-1: Increases the Monkey Ace's pierce to 8, from 5.
 * 1-1-0: Combines the faster attack speed and the exploding pineapple spawn (This is not recommend not only due to the pineapple tendency to miss its target, but it also locked the player out of the path that Path 1 Monkey Ace needs the most, which is path 3).
 * 1-0-1: Combines the increase in attack speed and pierce.
 * 0-1-1: Combines the Exploding pineapple spawn with the increase in pierce.
 * 2-0-0: Increases the amount of darts the Monkey Ace shoots, to 12.
 * 0-2-0: Allows the Monkey Ace to detect Camo Bloons, alongside a pineapple attack.
 * 0-0-2: Creates a new targeting option that allows the player to adjust the 'center' of the Monkey Ace Flight path, useful for 0-3-2 Monkey Aces.
 * 2-1-0: Combines the increase in attack speed and projectiles with the Exploding pineapple spawn.
 * 2-2-0: Combines the increase in attack speed and projectiles with the ability to see camo bloons.
 * 1-2-0: A 2-2-0 without the increase of projectiles.
 * 0-2-1: A 0-2-2 without the ability to change the 'center' of the Monkey Ace flight path.
 * 1-0-2: A 2-0-2 without the increase of projectiles
 * 2-0-2: Combines the increase in attack speed and projectile count with the increase a pierce and the ability to change the 'center' of the Monkey ace flight path.
 * 0-1-2: 0-2-2 without the ability to see camo bloons.
 * 0-2-2: Combines the Exploding pineapple spawn and increase pierce with the ability to see camo bloons and to change the 'center' of the Monkey ace flight path.

Fighter Plane

 * 3-0-0: Fighter Plane gains twin homing missiles that home onto MOAB-class and deal a chunk of damage to the affected targets. From Version 28.0, Exploding Pineapples now grants the missiles additional pierce and blast radius, thereby making the choice for crosspathing dependent on whether the missiles or darts are more desirable to be improved.
 * 3-1-0: Grants +2 pierce and +4.5 blast radius to the missiles, a fairly substantial buff that improves their grouped MOAB effectiveness by a decent margin.
 * 3-2-0: Grants camo detection on all attacks, which can be mildly useful, though other sources such as Radar Scanner and Level 8+ Etienne generally make this upgrade redundant. Note that this means the MOAB missiles can target DDTs despite not being able to damage them, which is rather detrimental.
 * 3-0-1: The pierce buff granted to darts is quite high, and thus it can be quite worthwhile to obtain this upgrade if wishing to focus more on the darts.
 * 3-0-2: Grants significantly more positional flexibility at the cost of micro potential, allowing the Ace to be placed anywhere. Useful for ensuring the missiles don't take awkward long paths when homing in on MOABs.

Operation: Dart Storm

 * 4-0-0: Operation: Dart Storm increases the number of darts from 8 to 16, doubles attack speed of both its darts and missiles, and increases missile damage. An uncrosspathed ODS is sub-optimal for the mid-game and is mainly used for its missiles as a way to counter MOAB-class bloons from any range.
 * 4-1-0: Pineapples are not deployed twice as fast. ODS still doesn't pop Lead, and so a heavily microed ODS with the Exploding Pineapple upgrade can be used to pop Leads. The main benefit, however, is the increased MOAB missile pierce, which becomes even more useful thanks to them being launched twice as fast and having more damage.
 * 4-2-0: Same reasoning as 3-2-0
 * 4-0-1: With the doubled dart attack speed and 4 extra darts, the extra pierce granted is made more significant than before, and so this crosspath becomes very lucrative.
 * 4-0-2: Much like with 3-0-2, the massive flexibility in positioning makes this upgrade quite useful for placing your Ace exactly where your defense needs it, and with the extra darts and double attack speed, having the Ace be able to be directly on top of the track no matter where the track is can be crucial.

Sky Shredder

 * 5-0-0: Sky Shredder gains excellent DPS against all kinds of bloons alike over a large area of a map, unobstructed by Line of Sight. Crosspathing isn't too impactful for Sky Shredder, but crosspathing does help maximize its full power.
 * 5-1-0: Pineapples are quite significant for Shredder since 28.0, since the massive MOAB damage of the missiles can be spread out across more MOABs.
 * 5-2-0: While generally towers like Radar Scanner and other decamo options are more effective thanks to the increased flexibility, since Shredder's MOAB missiles have quite high damage and are able to pop all Bloon types, there is an argument to be made that 5-2-0, while not having as much effectiveness vs Bloons, can become a significant threat against all classes of MOAB, including DDTs.
 * 5-0-1: A large increase of pierce for the Shredder, from 5 to 8. For most maps, this is the optimal crosspath.
 * 5-0-2: Generally the same as with 4-0-2, though with a caveat: Shredder's microed DPS potential is much more significant than previous upgrades, and purchasing Centered Path will tend to throw off muscle memory, causing its performance to be worse. If your ability to micro is solid, ignore this upgrade, otherwise, the flexibility can be useful.

Bomber Ace

 * 0-3-0: Bomber Ace exchanges sporadically deployed pineapples with bombing arrays that are only targeted on bloon tracks. This gives the Monkey Ace much more reliable lead-popping power and is a powerful source of grouped popping power. Maximizing its damage potential requires crosspathing. As for 0-3-0 Bomber Ace, this is mostly as either a stepping stone for just 0-4-0 Ground Zero for the ability only or as a stepping stone to 1-3-0 for the faster bomb deployment.
 * 1-3-0: Generally the best crosspath, seeing as the increased bomb drop speed gives quick dropping of powerful bomber ace bombs, which, when microed, can be very powerful damage.
 * 2-3-0: Not more useful than a 1-3-0 Ace, as it doesn't affect bombs.
 * 0-3-1: Adds extra pierce to each bomb, but since it is rare to reach the 20 pierce cap per bomb outside of Race Events the extra pierce rarely matters.
 * 0-3-2: In certain niches, long lines of 0-3-2 Bomber Aces can be used to bomb central regions of the track. In addition, 0-3-2 can be microed a little more freely around the map by having better flight coverage.

Ground Zero

 * 0-4-0: Often it's not useful to crosspath a Ground Zero, as it is most often used for only the ability, but it is still useful to crosspath it in cases where the bombs can do lots of damage or the ace will be microed.
 * 1-4-0: Generally the best crosspath, seeing as the increased bomb drop speed gives quick dropping of powerful bomber ace bombs, which, when microed, can be very powerful damage.
 * 2-4-0: Not more useful than a 1-4-0 Ace, as it doesn't affect bombs or ability.
 * 0-4-1: Like 0-3-1, adds pierce to darts as well as for bombs, but because Ground Zero bombs have heaps of pierce already and the attack speed is far more favorable, this crosspath is not very useful.
 * 0-4-2: Generally useless, but in niche scenarios where 1-4-0 wouldn't reach the track enough to make use of bombs, 0-4-2 could be used to enhance the coverage of the bombs.

Tsar Bomba

 * 0-5-0: Like Ground Zero, Tsar Bomba is mostly used for its powerful nuke ability. Again, crosspathing has no effect on its ability. Crosspathing is all about boosting its bomb attacks. Bear in mind that Tsar bombing arrays can pop Black Bloon properties, which is the only benefit it gains for its bombing array attacks.
 * 1-5-0: Like 1-4-0 Ground Zero, increases rate of dropping its Bomber Ace bomb arrays, for the maximum DPS potential with its bombing attacks.
 * 2-5-0: See 2-4-0
 * 0-5-1: See 0-4-1
 * 0-5-2: See 0-4-2

Neva-Miss Targeting

 * 0-0-3: Neva-Miss Targeting is reasonably accurate because its darts home towards bloons no matter where the Ace or its darts are. Crosspathing is a good idea to add to optimize its homing potential.
 * 1-0-3: Increases attack speed by +33% for faster rate of homing darts. May also increase reliability at hitting targets.
 * 2-0-3: Extra darts is far more valuable for Neva-Miss Targeting, considering that all darts home towards their target(s). This increases its DPS by a significant amount.
 * 0-1-3: Pineapples aren't very useful especially for Neva-Miss because pineapples still behave in their usual sporadically dispensed fashion.
 * 0-2-3: Gaining internal camo detection is useful, but it misses out on Path 1 for better DPS. It is recommended to use a Radar Scanner Village instead, unless on a tight budget.

Spectre

 * 0-0-4: The Spectre focuses all its quick darts and bombs into an intense single-target stream, greatly enhancing its single-target damage against MOABs and even BFBs in addition to having decent pierce against spaced rushes and discontinuous denser rushes alike. Usually Spectre is not bought without a crosspath inherited from Neva-Miss Targeting, however.
 * 1-0-4: Boosts Spectre's DPS by 33%, for maximum DPS potential. Often inherited by an optimized Neva-Miss.
 * 2-0-4: Increases the pierce of the Spectre's attacks, more specifically its darts. Usually inherited from Neva-Miss; if not, then it is generally not worth purchasing.
 * 0-1-4: Since 28.0, Pineapples have become something of a sidegrade for Spectre, thanks to their improving of Spectre's bombs' pierce. While generally attack speed is more valuable, in certain situations this upgrade can be useful.
 * 0-2-4: It's not worth trading significantly more DPS for camo detection. It is not recommended to buy this, rather one should use a Radar Scanner Village instead.

Flying Fortress

 * 0-0-5: Not only does a Flying Fortress shoot triple the amount of attacks, it attacks around +50% faster than Spectre and deals much more damage per attack. With exception of Flying Fortress Earliest Round CHIMPS challenges, a Flying Fortress is best crosspathed to make use of its immense damage potential.
 * 1-0-5: Increases attack speed by +33% for maximum DPS potential.
 * 2-0-5: Extra dart pierce via Lots More Darts is redundant, like 2-0-4 Spectre. It doesn't hurt to add this upgrade, it's just wasteful in terms of money.
 * 0-1-5: Pineapples do provide extra bomb pierce, but with the triple streams attack speed becomes even more lucrative, making it worse than 1-0-5 by a wider margin than 0-1-4 is compared to 1-0-4.
 * 0-2-5: Gains internal camo detection, allowing it can both hit and damage DDTs even without a Radar Scanner, thanks to its Normal damage type. However, Flying Fortress is super expensive and prefers external camo detection and the Path 1 crosspath.

Strategies
Except when dealing with the Bomber Ace path, the game presents crosspathing the Monkey Ace as a choice between either improved explosives and Camo Detection via Spy Plane or extra dart power from the other crosspath. It is generally recommended to always purchase the available crosspath that does not contain Spy Plane, since externally granted camo detection (such as Radar Scanner and Etienne) or decamo can substitute for Spy Plane, and popping power will be lost. There is one exception to this recommendation, however: the MOAB missiles of top path can appreciate the extra pierce in certain scenarios. Still, the only reason to ever buy Spy Plane instead of just Exploding Pineapple is during a custom challenge that bans all other camo-detecting options, or bans the other crosspath.