I ran a mega-encounter in my spheres campaign today.

The PCs (8th level) are currently travelling through an evil empire (they want to investigate something on the other side of the continent, and the empire has the best roads) and have heard a lot of rumors of how Drow are currently harassing the empire so much that they have issued a curfew and martial law in their cities. Staying at an inn in a major city for the night, they keep watch and notice a massive uproar and buildings going up in flames not far away. Being a fairly good aligned and heroic group they go to the rescue.

It is a new moon, so visibility is kind of bad. But one PC has a sword that lights up a 20-foot radius while another has a tattoo on his hand that creates a cone of light, and most of them have darkvision. The barbarian is running on the rooftops while carrying the gnome bard, the elementalist is flying, while the heavy armor incanter and the dwarf striker follow the streets. The encounter starts with the PCs noticing 4 Ogre Spiders clinging to the walls at the side of a street. While easily killing the spiders, they hear screams and explosions from inside the buildings at both sides of the street. The barbarian runs inside the house on his side of the street and find two humans who are bleeding out as well as a Minotaur and a goblin in the staircase. Meanwhile a 2nd Minotaur and a 2nd goblin attacks the party from the house on the opposite side of
the street.

One of the Goblins, trained in the alchemy sphere, throws an improved alchemist fire that puts both the barbarian and his Minotaur friend on fire while the Minotaur takes a nasty wound from the barbarian. The Incanter enters the house, puts out the fire, takes a bottled lightning to the face, and leaves the house. Then the Minotaur shoves the barbarian into the wall before bull rushing him through it twice (swift action bull rush). The bard jumps in through a window and heals the barbarian + humans who are bleeding out. Meanwhile out in the street, the striker grapples his Minotaur and throws him into the ground so well the Minotaur gets stuck.

At this point, two Orcs and a Flesh Golem round the corner and try to attack, only the Orcs all get disintegrated by the elementalist. The Flesh Golem proceeds to go berserk and starts murdering the Minotaur who is entangled by the street. After another round or so of cleanup, they hear lots of screams and see a massive shadow as a Giant Tarantula is charging down the street towards them. What they don't see is the invisible Drider who managed to sneak up behind them.

Unleashing a fully augmented Chain Shock blast, the invisible Drider hopes to catch the party by surprise but loses its natural 20 against the striker to a forced reroll from the bard and then completely misses due to a rebuff from the elementalist. Since the Drider is still invisible the barbarian charges the foe he can see (Giant Tarantula), avoid the attack of opportunity and deals massive damage plus some bleed. The bleed reduces the Tarantula to 0 hp, causing it to start dying after biting the barbarian (and denying the barbarian a recharge of his martial focus). The elementalist seeks cover inside a building while drinking a potion of invisibility (they exist in my game), and the bard follows the example by drinking his own. Realizing she is in a bad position, the Drider uses guided strike with an electric blast before starting to withdraw.

To the rest of the players great annoyance, the barbarian drinks his potion of see invisibility and pursues the Drider straight into the Drow ambush. Magical darkness is triggered by the drider arriving at tonight's Drow hideout. As a proper barbarian, he spell sunders the darkness but only manages to suppress it for 2 rounds, so before he knows it he is under fire from a Drow Sniper and an apprentice Drow Storm Priestess while a Drow Mageknight teleports up behind him to flank with the Drider. Seeing their barbarian is in a bit of a bind, the party rushes to his aid with all they got, and through lots of lucky rolls on his miss chance and with his Defensive Slice the barbarian somehow survives the drow ambush. It all ends with the striker catching the apprentice Storm Priestess off guard while the elementalist managed to knock the sniper into the waiting barbarian greatsword.