Line of Sight

Line of Sight (sometimes shortened to LoS) is a game mechanic introduced in Bloons TD 6. As its name implies, Line of Sight applies to most towers when interacting with their placement near obstacles, causing parts of their range to be obstructed and unable to be utilized at all. The effect is represented within the range of a tower with red in place of the dark gray that its range is typically represented as.

There are also instances where the affected tower has restricted lines of sight without any portion of its range being actively obstructed. This occurs when considering towers that utilize infinite range aside their actual range, such as the Sniper Monkey and Dartling Gunner's small range circle around itself versus its actual range that covers the whole of the map, which itself can be blocked by objects. A similar occurrence is present with the Advanced Intel upgrade for the Monkey Sub, gaining the representation of blocked lines of vision with or without a tower present in that blindspot.

Line of Sight also makes an appearance in Bloons Adventure Time TD, although to a lesser extent.

Objects
Objects are the group of structures and items present in BTD6 that serve to interfere with the Lines of Sight for towers placed in the game. They tend to be placed either on the outskirts of the map or near the center, as to minimize and maximize their presence as Line of Sight blockers. Another irritating aspect is that contact with any of these objects will cause projectiles to be used up, even if they had a high pierce that was still to be used on the bloons.

Most maps have at least some form of objects, with more prominent obstacles being a special sub-category of Removable Objects.

Permanent
Permanent Objects serve as the general sight line blocker for most maps, with the likes of Logs, Tree Stump, or Hedge using them to limit the potential of towers as well as making the tracks more challenging to justify their longer track lengths. Hence, most of the permanent objects that majorly obstruct the track are found in Beginner difficulty, though there are examples outside this difficulty.

Removable
Removable Objects are found mostly on Intermediate, Advanced, and Expert difficulty maps, functioning near-identical to normal objects except for one aspect: they can be paid for so that the area they inhabit can be transformed, often in the favor of the player. Most of these objects serve to only block off portions of the map to place towers upon, as well as most of the time obscure the sight lines of towers.

Some removable obstacles cause the terrain to be converted to another terrain. One such example is the removable object in #Ouch; when removed, it changes a water-filled hole in the center of the map into normal land, unrelated to sight lines, but purely conversion of terrain. The activatable button on Flooded Valley also converts terrain, except that it's conversion from land to water and it elevates the entire left-hand side of the map. Sunken Columns works like #Ouch except with two separate puddles.

List of Removable and Buildable Obstacles
There are a number of different removable obstacles that can be found in each map that can be removed for a specific amount of cash. Some will cost more depending on the type, but most will generally cost either $500 for smaller objects or $1000 for larger objects.

The Cabin (Total: $500) Skates (Total: $500) Encrypted (Total: $1000) Bazaar (Total: $2000): KartsNDarts (Total: $1000): Haunted (Total: $1000): Downstream (Total: $700) Firing Range: Cracked: Streambed: Chutes (Total: $700): Rake: Spice Islands: Sunken Columns (Total: $2000): X Factor (Total: $2000) Mesa (Total: $1500) Spillway (Total: $8000) Cargo (Total: $1000): Pat's Pond (Total: $2000): Peninsula (Total: $1500): High Finance (Total: $12,550): Another Brick (Total: $2000): Cornfield (Total: $9300): Flooded Valley (Total: $5000): Bloody Puddles (2) - $1500: Quad (Total: $6000): Dark Castle (Total: $4000): #Ouch :
 * Car - $500
 * Houses - $500
 * Altars (4) – $250
 * Trees (4) – $500
 * Haystacks with tire stacks (2) – $500
 * Trees (2) - $500
 * Rock piles (2) - $350
 * Watch Tower - $1000
 * Rock - $1000
 * Fossil Rock - $1000
 * Statues (2) - $350 each
 * Totem - $1000 ($350 before Version 2.0)
 * Palm Trees - $1000
 * Puddle (2) - $1000
 * "High ground pad" - $2000
 * Rock stacks (3) - $500
 * Inflatable walls (4) - $2000
 * Graffitied Trucks (2) - $500 (Note: Only unlocks at Round 40+)
 * Rocks (2) - $500
 * Bushes (2) - $500
 * Seaweed patches (3) - $500
 * Building north of bridge - $500
 * Building south of bridge - $750
 * Building with crane - $500
 * Dual buildings south of crane - $1000
 * Dual buildings east of left upper tall building - $1000
 * Building east of left lower tall building - $750
 * Small bottom-right building - $350
 * Southern-most building - $500
 * Small bottom-left building - $350
 * Small top-right building - $350
 * North-most building - $500
 * Left upper tall building - $1500
 * Left lower tall building - $1500
 * Right upper tall building - $1500
 * Right lower tall building - $1500
 * Palettes of Bricks (2) - $1000 each
 * Small Cornfield on left and right (2) - $350
 * Other Cornfields on left and right (2) - $500
 * Scarecrow Cornfield - $1000
 * Cornfield below and above Scarecrow Cornfield (2) - $700
 * Cornfield below small free space - $700
 * Top Square Cornfield - $1000
 * Long Cornfield at bottom - $1000
 * Large Cornfield - $1500
 * Dam Valley (activated button) – $5000
 * "Jeep" - $1000 (Note: Results in a false removal of the jeep, resulting in no removal of any obstacle, until the subsequently added obstacle is removed)
 * Broken Chinook and Jeep - $500
 * Floral Trusses (4) - $1500
 * Forest (4) - $1000
 * Puddle - $1000

Exceptions
As there are many towers afflicted with blind spots when combating alongside objects, there are several examples of tower that completely or partially bypass these obstacles.

Towers and Upgrades
Towers and upgrades that ignore line of sight.
 * Abilities, such as MOAB Assassin, Blade Maelstrom, and Dark Knight. Buff abilities such as Super Monkey Fan Club and Turbo Charge do not allow towers to ignore LoS, though the ability itself ignores LoS when choosing what to buff. There is a special interaction with Transforming Tonic and Total Transformation that actually temporarily loses Line of Sight for the transformed towers.
 * Buffs, such as Shinobi Tactics.
 * Full-map effects, such as Spirit of the Forest's vines.
 * Splash damage: any form of splash damage can ignore Line of Sight; Ice Monkey's splash ignores LoS, and so does Bomb Shooter bombs and any other form of explosive.
 * Monkey Ace
 * Heli Pilot
 * Alchemist
 * Mortar Monkey
 * Monkey Village
 * Spike Factory
 * Boomerang Monkey: Glaive Lord's orbiting glaives.
 * Tack Shooter: Inferno Ring's fireballs.
 * Monkey Sub: Submerge and Support, Bloontonium Reactor, and Energizer do not get obstructed by obstacles while their targeting is set to "Submerge", but their darts are obstructed.
 * Monkey Buccaneer: The Aircraft Carrier and Carrier Flagship gain the ability to ignore obstacles with their planes but not their regular projectiles. The Carrier Flagship also allows monkeys placed on top of the ship to bypass line of sight, with a few exceptions.
 * Wizard Monkey:
 * Path 1: Guided Magic (Arcane Mastery until Version 3.0) causes the tower itself to ignore LoS.
 * Path 2: Summon Phoenix's phoenix flies overhead, ignoring line of sight. This also applies to Wizard Lord Phoenix's permanent phoenix and the "super phoenix" transformation.
 * Path 3: Necromancer: Unpopped Army's reanimation ignores line of sight.
 * Druid: Druid of the Jungle's vines.
 * Engineer Monkey: Cleansing Foam's foam.
 * Super Monkey: Sun Temple and up ignores line of sight. Can also ignore Line of Sight with "X-Ray Ultra" MK active.

Heroes
(As of v27.3)


 * Heroes that completely ignore line of sight for all attacks:
 * Psi


 * Heroes that ignore line of sight for their basic attacks:
 * Obyn Greenfoot
 * Benjamin (Bloon Trojan)
 * Ezili
 * Adora
 * Etienne


 * Heroes restricted by line of sight for their basic attacks:
 * Quincy
 * Gwendolin
 * Striker Jones
 * Captain Churchill
 * Pat Fusty
 * Admiral Brickell
 * Sauda

Highground

 * See also: High Ground

On specific maps, there are certain locations where a tower or multiple towers can bypass any and all forms of objects, allowing for a good vantage point for towers that are most hindered, like the Sniper Monkey. Instances include the large stump in the center of Tree Stump, or the vacant crow's nest in Off the Coast.

Alternatively, Highground can be simulated by use of the Carrier Flagship, allowing towers placed upon it to bypass objects themselves, although some tall obstacles will still block the line of sights especially for the lower platform.

Dart Monkey's Crossbow upgrade raises its sight height above its previous and next upgrades, causing it to sometimes lose line of sight when upgraded to Sharp Shooter. This was (up until version 23) noticeable when placing a Dart Monkey on Flooded Valley, on the lower rocks close to the dam.

The Dartling Gunner is unique in having both autofire (can fire without a Bloon to hit) and line of sight. As of version 22, this allows it to shoot over/through some walls which block its line of sight, such as in Spillway. Bloon Area Denial System and above loses line of sight indication, but its projectiles still respect line of sight: it has four different guns with different heights, which each have their own line of sight for fire. Plasma Accelerator and above do not bypass line of sight, apparently having a lower firing height.

Bloons Adventure Time TD
Line of Sight mechanics in Bloons Adventure Time TD remain fairly similar compared to in Bloons TD 6. Most characters are affected by this, but Marceline and Hunter Marceline will both always ignore Line of Sight. When it comes to allies, Squadron and any other flying allies will always ignore Line of Sight.

Trivia

 * There was once a Line of Sight option in the pause menu, which hid both the range and line of sight of a selected tower. This option was intended to help reduce lag on lower end devices or in late game.
 * This does not exist in the Steam version though. It was also later removed in version 11.0 due to ineffectiveness to prevent lag.
 * Projectiles affected by Line of Sight will disappear upon impact with a physical obstacle. This may be based on a similar mechanic in the Roof levels of the original Plants vs Zombies game; in that case, non-lobbing projectiles will disappear upon impact on the steep rooftops.
 * Admiral Brickell's Mega Mine can seek targets through the objects that block line of sight, but the explosion is affected by it.