Kobolts are EMP variants of Kobold Fliers, added in the Spring Forward Update along with the Hex Thrower. They closely resemble Fliers, but are charged with electricity, like Cyborks. Similar to the Kobold Fliers, they divebomb into defences to deal massive damage when they take enough damage, or if a particular defence or Hero draws their aggro. Kobalts will target Towers if they are close by, ignoring barricades, auras and traps. If the Defences survive the attack, they will be stunned for 20-30 seconds, similarly to Cybork attacks. Notably, they spawn on ground lanes instead of air lanes, but can still fly over defences.
The mini-boss variant for the Kobolt is the Zapper. The Zapper behaves similarly to the Kobolt with the exception of the massive EMP radius, capable of damaging the core even from spawn in smaller maps. It is also unable to be stunned.
Since Kobolts tend to stay on lane, and target Defences, it is recommended that barricades are used to tank the damage, or if you can kill them quickly with Defences and Hero burst damage. Try to space other defending towers from your barricades so that the EMPs will not disable them.
The Zapper mini-boss will target towers over other defences, so it is recommended to use auras and traps to quickly kill it before it can aggro and detonate onto other towers. Removing other nearby towers may help to keep the Zapper on track.