The people they are fighting are a merger of many anti-PvP guilds, whose players inevitably suck, but there are many of them. They called their new guild the Zealous Elite Righteous Guardians...
Also this one for basic tactics behind zerging and rushing in general.
King Rodericke's subjects in Charby the Vampirate stream out of the caves in which the Vampire Kingdom resides in waves to take on Zerlocke. Unfortunately for them he is functionally immortal, luckily for Rodericke he's not actually trying to defeat the Kingdom.
Ctrl+Alt+Del: "Achievement Unlocked — Way to play like an asshole, asshole."
In Girl Genius among its many, many other defenses, Castle Heterodyne can resort to unleashing every clank and construct abomination in its bowels at an aggressor.
Agatha's Dingbots tend to use this when making repairs or otherwise assisting her. They are individually tiny and only have one or two tools each but there are a lot of them and they seem to have a Hive Mind of sorts so they can work together to solve quite complex problems.
In the Sluggy chapter "Aylee", this seemed to be the only tactic the "ghouls" in an alternative dimension had against the humans. The humans had high-tech weapons, but were still somehow driven into exile in orbit by the sheer numbers which the unarmed ghouls could muster to rush at them in. They also used this tactic in the decisive final battle when attacking a critical point.
As evidenced in thisHomestuck Page ("HB: Waste exactly four hours on this tomfoolery"), the primary tactic of Felt members Eggs and Biscuits is to use their respective time-traveling implements in tandem to swarm enemies. With themselves.
Much later on, Vriska and Meenah, two Trolls, are raising up a Ghost Army to bring down the Big Bad, who happens to also be a Physical God.
The First Empire's invasion of Ziragalen in Second Empire. When first seen from afar, there are so many Daleks massed in the first strike, they are mistaken for a storm.
Stand Still, Stay Silent: The crew has to deal with a horde made of ghosts and trolls in Chapter 13. The trolls are individually easy to kill, but only about half the crew of six is available to do so, and more just keep coming. Lalli has to deal with a stronger ghost that Reynir's new protection runes are unable to keep away, while Reynir himself has to stay hidden along with Tuuri because being around trolls is much more dangerous for them than for everyone else.
Schlock Mercenary: The resurrected ancient oafans have enough warships that they were able to find a top-secret battlefleet by using a brute-force search pattern on the entire galaxy.
Descension Fleetarch: If it makes you feel any better, you were in the last place we looked.