To beat Bloonarius in Bloons TD 6, a solid strategy revolves around efficient early-game farming and a strong tiered defense setup that scales with the boss's increasing difficulty. Here is a detailed approach based on community tips and tutorials:

Early Game Farming

• Start by placing a Banana Farm and upgrading it to generate income quickly.
• Use a combination of Monkey Buccaneers (Merchantman boats) upgraded to Grape Shot and Favor Trade to maximize early cash flow.
• Continue placing and upgrading farms (preferably 0-2-4 farms rather than 4-2-0 near the boss round) to build a strong economy before Bloonarius arrives

Tier 1 Strategy

• Place a Boomerang Monkey upgraded to 0-2-4 (More Glaives and Red Hot Rangs) for consistent damage.
• Add a Ninja Monkey upgraded to Ninja Discipline and Sticky Bomb for burst damage.
• Support these with an Alchemist upgraded to Berserker Brew to buff your damage dealers.
• Keep placing more Merchantman boats until space runs out, upgrading them to Hot Shots and Favor Trade for extra cash and damage

Tier 2 Strategy

• Add a 1-1-5 Monkey Ace (Mad) and use its ability against Bloonarius.
• Upgrade your farms and continue farming aggressively to prepare for higher tiers.
• Consider a Glaive Lord on a corner for shredding BFBs if applicable

Tier 3 and Beyond

• Place a 1-5 Dart Monkey and upgrade to Dart Paragon if possible; the Dart Paragon is very effective against Bloonarius.
• Use multiple Dart Monkeys and Ninja Monkeys with buffs from Alchemist and Village.
• Use a VTSG (Very Tall Spiky Genius), Super Mines, and other high-damage towers as you reach Tier 4 and Tier 5.
• Place a Super Brittle tower and 2-5-0 Glue Gunner to increase boss damage.
• Use a Cripple MOAB (5-2-0) targeting strong for slowing Bloonarius later in the fight

General Tips

• Always build and sell next to a 2-0-4 Buccaneer boat if possible to maximize efficiency.
• Use Overclock on a 0-0-0 farm to boost income early, then sell and upgrade farms accordingly.
• Exit and re-enter the game mid-round if you get a penalty to optimize your setup.
• Use abilities like the Mad Monkey's ability and Overclock strategically to maximize damage output.
• Focus on gradual damage and sustain rather than burst damage alone, as Bloonarius spawns many bloons that need clearing alongside the boss

This approach balances farming, damage, and utility towers to handle Bloonarius's phases effectively. Watching detailed video guides can also help visualize the timing and placement of towers for specific maps