Chaos is the replacement for Nightmare difficulty however with different mechanics and enemies. Players will need to utilize the new Shards system, Ascension, and strategize in hopes of beating the new Chaos difficulty.
Each Chaos tier introduces new enemy.
In C1 you will first encounter Vanguards - shield goblins. Tthey have very high resistance to direct front damage, best strategy against them is to use traps, auras, magic towers (like Ramster or Flamethrower) or build direct damage towers behind them.
Cyborks are an anti-trap/aura/node enemy inctroduced in C2. If you’re attempting to take down Cyborks with these defenses, you’re going to have a hard time.
Shield Geodes are introduced in this tier, they are reflecting projectiles with energy shield, strategies against them are similar as agains C1 Vanguards, but because they have shield around them, placing towers behind won't work. Because best way of beating them is so similar as beating Vanguards, they will be present in this Chaos tier as well.
This Chaos is centered around the Berserker Orcs (commonly called "Lady Orcs"). Berserkers are all about being fast and dealing high damage upon reaching defenses, so using things like stuns and knockups to slow them down are your main counter for this threat. Cyborks counter most of those kinds of effects, so you won't see Cyborks in this Chaos tier anymore, but there will be Shield Geodes and Vanguards present.
Chaos V is all about Dark Assassins. They are sneaking up on you and after short period after purple fog gathers around you - they will teleport to you and deal great amount of damage silencing all your abilities attacks, only thing you can do is run around and activate pet ability. Best way to get Dark Assassin off your back is to run to your defenses/friends so they can kill it, activate immunity pet skill or stun them. Most popular way is to use some Cannons with Stun Fire or Heavy Cannonball shard in par with Sharpened Spikes shard on blockade. Assassins attack in cone, so you can easily fail the map by running around defenses or Core with Assassin on your back. In this tier you will also encounter Cyborks, Berserker Orcs and sometimes single Shield Geode per wave (usually can spawn in wave 3 and later ones), it's crucial to check where it will spawn and kill it as fast as possible on this difficulty level.