Sam, after traveling back in time, returns shortly after and reports that "The First Encounter didn't go so well.". So, he is sent into the future in order to assassinate Mental. After finding an ally, Sam fights off hundreds of monsters on his way to Mental's temple. But instead of Mental, he finds another ally. The trio exits the temple, only to be ambushed by Ugh-Zan. He chased them all the way to the Pyramid, and even when they go aboard the spaceship. The trio manages to kill Ugh-Zan, and nothing is known from that point.
Serious Sam: The Random Encounter is a sidescroller 2D RPG-like game. From time to time, when moving a block in the "real" world, there's a chance you'll encounter random enemies. You can't encounter enemies in blocks you've already did so before. While fighting, you have as much time as you want to prepare; you can either command one of your Sams to fire, switch weapon or use an item. Each weapon has a unique firing mechanic, switching weapons takes a short time and when using items, your Sam can't use or switch weapons. After you're done, the game switches to real-time mode, where you have 5 seconds of real-time action. You can move your Sams up and down while in real-time. Destroying all the enemies finishes the round and fills the progress bar further. When the progress bar is full, you get a new item. Your health is also restored to full when finishing a round.
You can either choose to play the single player campaign, which is consisted of 3 chapters, each one with 3 levels, or play the Endless Mode, which pretty much explains itself. You can have up to 3 save files for Single Player, but you can delete them from the Options menu.
Arachnoids, in early encounters, come in small numbers, but they continue to grow in larger and larger numbers. They only try to come close to you when they're far away, but when they're close enough, they try to keep a short distance and shoot rapidly at you until you get some distance or they die.
Rocketeers aren't a big threat, even when in large numbers, unless they start shooting.
Firecrackers are a bit more dangerous than Rocketeers, as they fire 5-6 projectiles at the same time, making it hard to evade them.
Gnaars are a little-to-no threat to the player, as they only charge in to come close and impact with the player. They should be easy to kill.
Same as normal Gnaars, but they just fly, making it easier to reach the player.
Same as normal Gnaars, only "invisible" (no color, only their outlines are visible).
Harpies will switch from walking to flying occasionally, they will land in the start of a real-time round, and then take off a bit later. When walking, they simply charge towards the player. When flying, they instead shoot projectiles.
Kamikazes are very dangerous, as they are very fast and should be eliminated ASAP. Underwater Kamikazes are even faster than Ground Kamikazes, making them even more dangerous.
Kleers will constantly charge at the player, and sometimes shoot bone projectiles. They are a mediocre threat, depends on what other enemies are around.
Minor Mechanoids will try to come close to the player, and will shoot a burst of laser beams while doing so. They will not impact with the player, and will try to keep a small distance.
Reebans will try to get close to the players, and sometimes impact with them. They are very dangerous, as they will constantly and rapidly shock any Sam near them until they are dead, and should be eliminated from range.
Small Lava Golem
Small Lava Golems are not much of a threat, but will shoot projectiles at the player from a distance. Fortunately, they can be destroyed. The first Small Lava Golem is encountered as a "boss" fight in World 1-3.
Werebulls are very fast, and will try to impact with the player, dealing heavy damage. They should be disposed of as soon as possible. Although, they can easily be evaded by moving up and down.
The Highlander is not very dangerous, he won't take too much damage, but he'll try to get close to the player. It is suggested you use Serious Speed when he's too close. He'll also shoot fireballs at the player.
The Major Mechanoid is very dangerous, as it will the player very fast, and will shoot a burst of lasers which can kill 1-2 Sams in one real-time round. Keep as much distance as possible and shoot it down with rapid-firing weapons.
Big Lava Golem
The Big Lava Golem has a lot of health, and will shoot giant projectiles at you, but like Small Lava Golems, they're destructible. He's followed by a horde of Small Lava Golems as well. He's quite a threat, but his Small Lava Golem army is even more of a threat. Destroy him fast with a rapid-firing weapon (such as the Minigun) under Serious Damage to get the fight done with.
Hoppers are very weak, can be killed with one shot fro manything. But they come in very large numbers, and will kill a Sam very fast if multiple of them impact with him. After you clear a Hopper wave, another one will come, which makes them rather dangerous.
Tentaculus will try to damage you by swinging its tentacles to the upper or lower part of the screen. You will be safe while you're in the middle. But it will also open its mouth(s) to spawn a swarm of Reeban Electro-Fishies, making him a tough boss fight. He can also take a lot of punishment. Make sure to kill him AFTER you get the keys to the exit of World 2-3, so you won't have to kill him again.
Ugh-Zan, in the final boss fight, is followed by a legion of very dangerous enemy combinations, such as Minor Mechanoids and Arachnoids. If you have 2 cannons and a Serious Damage, then shoot him with whatever weapon you wish for one round, let the cannons charge, then when they're about to fire (make sure they're aiming for the upper left corner of the gamescreen), use Serious Damage. The 2 cannonballs will be enough to kill him. Otherwise, use the Cannon and explosives, but keep the other enemies at bay.
These werebull-like creatures can be found if you find the secret teleporter in World 2-3 (it's on the lower left corner of the screen, just walk past the wall). They behave like werebulls, only though they deal more damage. Destroy them quickly, and walk up to the crates near their encounter location for some goodies.
Your basic weapon; you start with them. After finding the shotgun, they lose their effectiveness. After you find the Minigun, they become useless.
A rather long-ranged Shotgun for a Serious Sam Shotgun. You can switch its radius, but it will spread more and more the more you increase it. At point-blank range, it's very lethal, but it's still reliable for medium-ranged combat.
A very powerful weapon, at first, it charges up, then it begins firing rapidly in a line, dealing a lot of damage to small and medium enemies. When accompanied with Serious Damage, it's the best boss killer as well, along with the Laser Rifle.
Shoots 3-4 rockets in a cone in front of Sam. The rockets are high-damaging, and have splash damage, and are reliable against bosses and medium enemies.
The Grenade Launcher fires a grenade in an arc which instantly explodes when reaching its fired location. It will deal major damage to all enemeis within, but is rather unreliable because you have to predict where enemies will move. So, it's better used against masses of enemies rather than just single ones. Especially fast ones.
The Laser Rifle shoots 3 laser beams in front of it, in a line, which deal decent damage, but what makes it good is the fact that it slows enemies down (albeit in the game it says it "pushes them back"). Definitely one of the best weapons in the game when enemies are getting too close.
The Sniper only shoots one bullet, but kills any non-boss enemy it comes in contact with. Shoot lined up enemies to use the Sniper at its maximum efficiency.
The Cannon takes one turn to charge up, but after it shoots, it will instantly kill any enemy it comes in contact with, and it will also heavily damage Ugh-Zan. With Serious Damage, one Cannonball will destroy 50% of Ugh-Zan's health.
Gives full armor to the Sam that uses it. Better not used when you're being attacked by multiple enemies.
Gives full armor to ALL Sams.
Heals all Sams to full health. Better used when your Sams are about to die or too low on health.
Revives a Sam. Best used when enemies aren't shooting at you much.
Makes Sams run backward MUCH faster. Make sure to preserve one for the Highlander and Major Mechanoid. Also use it when you're close to death and enemies are about to impact with you, or there are too many projectiles.
Quadruples all of your weapons' damage. Best used against swarms of enemies or bosses with a rapid-firing gun, such as the Minigun.
Instantly kills all non-boss enemies. Best used when you're overwhelmed and can't handle the situation.
Summons 100+ kamikazes. Best done when you have another rapid-firing weapon firing in the meantime, else, the Kamikazes will reach you, and most likely kill you. Also, their explosion will damage nearby enemies, including other kamikazes, creating a chain reaction of explosions.