Erosion

Map overview for strategy

Erosion is a map you plan backwards from round 90. The last lane is tiny, sits next to the permanent glacier and lasts the whole late game, while every land tower you place on melting ice has an expiry date.

General rules:

• Long range, small footprint. Snipers, Subs with Advanced Intel, Mortars and other global or long-range towers keep working as lanes move.
• Permanent spots only for permanent towers. Put Villages and your win condition on the glacier, on water, or on Arctic Wind ice platforms.
• Disposable early towers. In early rounds, cheap towers like 0-0-0 Dart Monkeys on the first lane are fine, as long as you accept losing them at the end of round 17.
• Mobility helps. Corvus' Spirit Walk, Support Chinook's Redeploy, Dark Knight and teleporting heroes can move towers before the ice disappears.
• Arctic Wind platforms let you save land towers. Several water-placed Arctic Winds in range of each other can create enough ice to keep land towers alive and even hold a Heli Pilot.

Best towers

• Monkey Sub 2-0-2 (Advanced Intel plus Airburst Darts): shoots anything within range of your other towers, so it adapts to every lane change. A great early-game carry; 2-0-4 later for more damage.
• Sniper Monkey: 0-3-x Bouncing Bullet for the early and mid-game, 4-2-0 Maim MOAB for blimps. Snipers on the glacier never need to move.
• Spike Factory 0-5-2 (Carpet of Spikes): on the round 90+ lane its spikes are extremely concentrated, sweeping DDT rounds, cracking ZOMGs and erasing round 100's BAD. Use the 0-5-2 crosspath so spikes are not wasted on inactive lanes, and give it DDT popping power with MIB or Embrittlement.
• Dartling Gunner 0-0-5 (Bloon Exclusion Zone): the long mid-game lanes give you time to save for it, and once built it handles the late game if you add lead popping.
• Ice Monkey 0-3-x (Arctic Wind): creates ice platforms, slows ceramics cheaply and survives erosion.
• Druid 1-3-0 (Druid of the Jungle): long-reaching early and mid-game damage.
• Monkey Village 2-3-0: on the glacier, giving MIB to your late-game defence.

Best heroes

• Corvus: his Spirit and Spear hit from anywhere, and from level 7 Spirit Walk lets him move away from collapsing ice. His spellbook can bank a lot of cash for Carpet of Spikes or Bloon Exclusion Zone.
• Psi: global attacks and abilities from any spot, including the glacier. Steady support damage while you save.
• Geraldo: long-range utility through his shop items, and a common CHIMPS pick.
• Pat Fusty: he floats when his ice melts, so he never gets sold.

Easy and Medium

Outside CHIMPS, erosion only sells your towers for cash, so it is not a disaster. Use cheap towers on lane 1, a Sub 2-0-2 in the water, and Snipers on the glacier. From lane 2 on, keep most new spending on water and the glacier, and add a Perma-Spike or Carpet of Spikes near the final lane before round 90. Banana Farms and Merchantmen are good ways to fund this outside CHIMPS and Half Cash.

Hard

On Hard, follow the same plan but build Arctic Wind platforms early on the water near lanes 5 and 6 so you have stable space for a Village, a Spike Factory and support towers in the late game.

CHIMPS

In CHIMPS, spend as little as possible on land that will sink. A practical plan:

1. Round 1: a Monkey Sub in the water near lane 1 and a Dart Monkey next to the track. Place Psi or Geraldo where they will not drown (the glacier or water-safe spots).
2. Rounds 2 to 17: Sub to 2-0-2. Add one or two 0-0-0 Darts on lane 1 if you need them. Start a Sniper on the glacier.
3. Rounds 18 to 35: Sniper to 2-2-0 on the way to Maim MOAB, and a second glacier Sniper going 0-3-2 Bouncing Bullet if the lane needs more pierce. Add a Druid 1-3-0 if you have a safe spot for it. Make sure camo is covered by round 24.
4. Rounds 36 to 53: Sniper to 4-2-0 Maim MOAB for blimps. Place a Village on the glacier and build Arctic Winds on the water near the later lanes.
5. Rounds 54 to 89: grow a second Sniper or Sub damage source and start saving. Use Arctic Wind ice to hold a Spike Factory next to the final lane.
6. Rounds 90 to 100: finish Carpet of Spikes 0-5-2 on the final lane with a 2-3-0 MIB Village or Embrittlement for DDTs. Add MOAB Press or extra Arctic Wind slowdown for dense rounds. Carpet's ability handles round 100's BAD.

Impoppable

Impoppable is much easier than CHIMPS because selling is allowed and eroded towers refund cash. Use farms early, then build the same final-lane setup.

Dangerous rounds on this map

• Rounds 18, 36, 54, 72 and 90: the first round on each new lane, often with towers you just lost. Prepare the new lane before you finish the previous round.
• Round 63: a ceramic rush on lane 4.
• Rounds 90 to 100: the shortest lane in the game, so DDTs and ZOMGs exit very quickly.
• Boss Events: bosses always use lane 3.

The BTD6 Master YouTube channel has video guides for Erosion, including how to survive the lane changes.

Frequently asked questions

When does the ice melt on Erosion?

At the end of rounds 17, 35, 53, 71 and 89. The track then moves to the next lane, and no more ice melts after round 89.

What happens to towers when the ice melts?

Land towers on the melted ice are sold automatically, or lost in CHIMPS. Pat Fusty, Ice Monkeys, Mermonkeys and Sun Temples float, and towers on Arctic Wind ice survive.

Can you place a Heli Pilot on the glacier in Erosion?

No. The glacier artificially blocks Heli Pilots, although a Banana Farm or up to three Villages fit. Arctic Wind platforms can hold one.

What is the best hero for Erosion?

Corvus is very strong because his Spirit Walk avoids melting ice. Psi and Geraldo are good long-range alternatives.

How do you beat Erosion CHIMPS?

Keep early spending minimal, rely on a 2-0-2 Sub and glacier Snipers, build Arctic Wind platforms, and finish with Carpet of Spikes 0-5-2 plus a MIB Village on the final lane.

Is Erosion the hardest Advanced map?

It is one of the hardest, alongside X Factor and Castle Revenge, mainly because towers are lost to erosion and the final lane is extremely short.