Spectre is the final upgrade on path 1 for the Monkey Ace in Bloons TD 5. It costs $15300 on Easy, $18000 on Medium, $19440 on Hard, and $21600 on Impoppable. It makes the plane continuously fire bombs and darts very quickly directly at the bloons instead of firing eight darts. The bombs can pop lead bloons and black bloons. With the Spy Plane upgrade, they can target any bloon or MOAB class bloon within range and can easily destroy ceramics, rainbows, and other bloons that result from MOAB class bloons.
With a update, the bombs from the Spectre pops 2 layers of Bloons instead of 1. As a result, the Spectre is now hands-down the cheapest effective tower against non-MOAB class Bloons.
It doesn't have target priority and just shoots whatever's closest. To counteract this, it's better to place it off to the side so that the Bloons are always coming towards it. That way, it will generally target "First". However, it stops shooting if the plane flies too far off-screen.
One Spectre can destroy a MOAB easily, unless there is more than one spaced out, due to the fact that the bombs explode in a short radius, and can damage about 1 or 2 MOABs. Only the sharp darts are able to attack more than one.
Note that a 4/2 Spectre by itself can damage a DDT. This is because though a Spectre can pop black bloons and leads bloons by shooting bomb shells that can hurt any bloon type, so a DDT is not immune to this tower. However, adding Monkey Intelligence Bureau next to a Spectre's landing base is strongly recommended because then the Spectre will effectively become twice as powerful against DDTs because Monkey Intelligence Bureau allows also darts to damage DDTs.
The design of a Spectre Monkey Plane can also represent a theme called "Defending Our Skies".