Spike Pile

Spike Pile is an attack style characterized by its projectiles being a lump of damage by the use of a visible set of spikes. A true projectile with the Spike Pile property will lose "health" every time a bloon collides with them almost instantaneously. The "health" of a projectile with the Spike Pile property is determined by its pierce (e.g. a spike with 5 pierce can hit up to 5 individual bloons). It is part of the damage types family. Spike Factories have this by default.

Spike Pile is represented on Bloons Wiki as, the upgrade icon for Bigger Stacks in Bloons TD 6, as this depicts a pile of many spikes. Spike Pile automatically has Contact Damage but noticeably fast enough to block any bloon from skipping over a projectile with this property under normal speed rules.

Spike Pile is core element of Spike Factories as they have this attack style as a base tower. Caltrops is another example of such. Chemicals and magic cannot count because they often are status-related, usually do not continuously contact the same projectile, and most importantly do not resemble spikes at all.

Categorization cases
All attacks that are considered Spike Pile:
 * All Spike Factories have Spike Pile by default and will always have this property unless spawned from a Burst (e.g. Spiked Mines explosions).
 * Caltrops is considered Spike Pile because they work like Spike Factory spikes and look like such. Caltrops act as a lump of damage like what Spike Factory spikes do.
 * Obyn Greenfoot's Brambles is considered Spike Pile for the same reason as Caltrops.
 * Icicles is considered Spike Pile because bloons that contact the icicles can be hit multiple times like a Spike Factory spike pile.

Attacks that resemble Spike Pile but are not true Spike Pile:
 * Bloon Trap is not considered Spike Pile because bloons are instantly trapped into them and do not look like spikes.
 * Wall of Fire is not considered Spike Pile and instead is considered a projectile with Contact Damage . It does act like a lump of damage, but does not wear out like a true Spike Pile nor visually appears like a spike pile.
 * Gwendolin's Cocktail is not considered Spike Pile for the same reasons as Wall of Fire.
 * Sauda's Leaping Sword on-track swords are not considered Spike Pile because they don't look like spikes and use Contact Damage like Wall of Fire. It does act like a lump of damage, does still wear out like a true Spike Pile, but does not look like a spike pile and it acts more like a pierce-limited Wall of Fire than a spike.
 * Relentless Glue's glue track blobs are not considered Spike Pile because bloons can only hit the same blob once, even if the glue blobs gain more pierce.
 * Acid Pools are not considered Spike Pile because it is a chemical and cannot rehit the same bloon more than once.