Josh's Constant

"B-B-Beat any Expert Map on CHIMPS with $40,870 or more spent on 1 Spike Factory"

- BTD6 description

 is a secret achievement in BTD6. It can be achieved by completing CHIMPS Mode on any Expert Map with a single Spike Factory valued at $40,870 or greater. Earning this achievement will reward one 0-0-3 Spike Factory. This achievement will not be visible until it is achieved.

Tips

 * Just a single non-discounted 0-2-5 Perma-Spike is sufficient enough to gain this achievement. Therefore, Monkey Business or Monkey Commerce should not be bought for the whole Perma-Spike at all.
 * Alternatively, using a 2-5-0 Carpet of Spikes will work too, as it is the only other Spike Factory upgrade that will allow surpassing the $40,870 point while still being a useful Spike Factory upgrade.
 * Attempt this challenge on Dark Castle, if using the 0-2-5 Perma-Spike. Alternatively, play on Infernal, but take into account the extra lanes on the map. Sanctuary is another map where a Perma-Spike is viable in terms of practical means, but it is not as easy as the other two.

Strategy
In order to complete Josh's Constant as easy as possible, follow a standard Dark Castle CHIMPS meta strategy. It will involve a rather one-dimensional strategy plan, but it is unfortunately the only easy way out for Dark Castle CHIMPS early-game.

Start with a 0-0-0 Dart and a 0-0-0 Sub, where the 0-0-0 Dart is set on Strong is just met by adjustments towards the left. The 0-0-0 Sub should be on Strong to catch any faster Bloons, and sometimes on First to catch any strays. Save up for Obyn Greenfoot, or upgrade Sub to 0-0-1 if struggling. Near Obyn, place a 0-0-0 Ninja Monkey towards 0-0-1. Afterwards, save up for a 3-0-2 Ninja into 4-0-2 plus a 3-0-0 Alchemist nearby the Ninja. Upgrade Alchemist to 4-0-0 once affordable.

Finish a decent mid-game strategy as usual, but now add a 0-2-3 Spike Factory near the end of the map with no discounts. Pair with 3-0-0 Alchemist to increase chances of surviving with this Spike Factory type. Continue saving up for 0-2-5 Permaspike while still managing mid-game with little issue. Be aware of Round 63 though, as it's extremely unlikely that Permaspike can be bought before such a round can arrive. Use standard anti-Round-63 measures as usual; 1-0-0 or 0-1-2 Ice are both good options for stalling bloons off each side, while 2-0-4 Recursive Clusters and 4-0-2 MOAR Glaives are excellent at overall group popping power. But by using standard meta strategies, which usually utilize discounted Sun Avatar + Overclock to beat much of mid-game, Round 63 should not be a big problem otherwise.

Trivia

 * This achievement is named after the BTD6 player Jajajosh, known for creating various CHIMPS Mode strategies with various combinations. On his YouTube channel, he typically showcases CHIMPS Mode on hard maps using various different Heroes, Tier 5's, or with extra challenge modifiers added to CHIMPS Mode. He is most known for beating every Expert map in the game at the time in CHIMPS mode with Permaspike.
 * $40,870 is exactly how much it costs to purchase a 0-2-5 Perma-Spike on CHIMPS without discounts.