Ebbtide has no named infected subtypes, no specials, no elites and no bosses in the enemy sense - there is no bestiary in the game, and no published list of variants. What is documented is the behaviour of the horde itself, and that behaviour is enough to shape every decision you make.
The baseline threat is a mass of thousands of individually rendered pixel-art infected, swarming over bases and tanks. The claim on the store is a scale of roughly one million zombies against humanity's last carrier strike group. The relevant point is not the number but the behaviour: they arrive as a mass, they stack, and they keep coming while you are reloading.
This is the defining behaviour and the one that changes how every base must be built. The infected use each other's bodies as footholds to scale walls and rooftops. A wall therefore does not stop the horde - it slows it and gives it a ramp. The counter is concentrated fire at the base of the mass, where breaking the supporting bodies brings the climbers down.
Low-hovering helicopters can be boarded by infected. This makes your aviation support a conditional asset rather than a safe one - altitude is a defensive decision, not a detail. Keep them high, or provide escort suppression for the ones that need to descend.
Your own dead re-rise as zombies. This makes casualty count a strategic number rather than a morale number: every soldier lost permanently increases the size of the force opposing you, and their bodies contribute to the climbing mass at your wall. It is the reason a losing engagement gets worse the longer it continues, and the reason disengaging early is often correct.
The horde is a numbers problem with a specific shape, not a roster of enemies. You win by funneling that shape into a kill zone, breaking the climb before it completes, and never letting your own dead accumulate next to your walls. Fire discipline matters more than firepower, and retreating a beaten position early matters more than holding it.