Late game viruses tend to involve filling your Navi's half of the arena with area-consuming attacks and harmful panel types, which are meant to throw you into the paths of other virus attacks. Various enemies can make appearances in separate games, and so are sorted by their debut games.
- Cloudies spring into the air and spit out a cloud that zooms to Mega's current spot and floats up and down, barring Mega from that column. When combined with Swordys, they are the stuff of nightmares, as Swordies move incredibly fast and have long-ranged swords swipes (and in the first game, fighter-range, too). If a Cloudy cuts off access to Mega's back column, he'll be caught almost permanently in range of Swordy attacks.
- Swordies get kicked a fair bit down the totem pole in later games, though they're still not to be taken lightly. They can quickly approach the front of your field to attack with swords of varying ranges, and some even carry Area Grabs in case you had the idea of camping at the back where they can't reach you.
- The Ratty virus are mice that shoot bombs that slide along the floor and try to turn towards you like Magnet Man's magnets. What's troublesome about those mice is that they become extremely fast when they're low on HP. Not only that, but they always avoid standing directly in front of Mega Man. You better delete them on a single hit or you'll suffer.
- Megalian (or Heady in 6). These are the classic Battle Network demonic spider, viruses that are cloaked in auras and warp around their field a few times before launching their heads at Mega to bludgeon him with. Higher levels of Megalians have tougher auras with a different elemental weakness and farther reach.
- Beetank1 and Beetank2 aren't so bad, as they will only hit a 3-vertical area or a cross-shaped area respectively with their attacks. Beetank3 on the other hand launches bombs that hit a 3x3 square area for pretty hefty damage (140 in the first game, 80 in the second), meaning that you'll be forced to move at least twice to avoid it. If they target the center square and you haven't used an AreaGrab, it also becomes unavoidable damage right there. There's also a particular encounter formation that contains two of them, which will make dodging very frantic.
- Satella Viruses will launch a crosshair that will move around your side of the playing field, square by square. If this target contacts Mega's square, the virus will assault Mega with a chasing machine gun at a very fast and accurate rate. Their attack hits quickly, ignores Mercy Invincibility and deals high damage per hit, forcing you to move around (and into other Virus attacks) often. Later variants have their tracking crosshair move around extremely fast and they deal 160 damage per hit, meaning that you really don't want to be targeted at any cost.
Battle Network 2
- The second and third games feature Scuttles, which are practically demonic armored elementally-aligned deathray-shooting robotic spider viruses. The green ones sprout vines that move across the field and crush you, dealing lots of damage, requiring obscene amounts of Button Mashing to get out of, all the while holding you still so the others can murder you; the blue ones spit guard-breaking ice cubes that clog up the field FAST; the red ones shoot fire towers insanely easy to faceplant into dodging everything else; and the yellow ones call down lightning with completely unexpected timing, which are also easy to faceplant into if dodging too fast. The white ones skip fancy elemental patterns and simply shoot DEATH RAYS OF DOOM. All of them possess Auras which, unlike the Megalian viruses, don't have any elemental weakness and require a hit of 100 damage or more to break, making it difficult to take them out in a timely manner. And, yes, they are regular random encounters in the later areas of the Bonus Dungeon of those games.
- In the Bonus Dungeon of the third game, it is very likely the player can unwittingly stumble upon one of the two pre-determined encounters with them near the entrance when trying to obtain the chip that summons them. It can easily become an uphill fight for those not privy to this encounter.
- Dominerds can be this when accompained by other viruses, especially in Battle Network 5's Liberation Missions, where you have to clear the enemies under a tight time limit. They are very resistant to damage, either taking 1 or 0 (depending on game) unless it's from a breaking attack or when they are attempting to attack. Some high-level Dominerds pack Geddon-chips, which will crack all field panels. They won't suffer from this. You will.
- Stronger versions of the Dominerd in the third and fifth games amplify their frustration factor. Now, instead of pacing up and down one column, they turn invisible and sit in front of a random virus. You probably won't know where it is until either it's too late or you've already extinguished everything else.
- Puffballs and their palette-swapped upgrades Goofballs are masked Wood viruses that slowly approach Mega's boundary. When they reach the edge of their field, they hold their masks out one panel and flood all adjacent panels with poison gas. On top of that, they can use Panel Grab to slowly encroach further into Mega's territory. If you think that you can hang back out of reach and just shoot at them from afar, be warned: those masks double as shields that will render most projectiles useless.
- Sparky (or Shakey, in the 5th game) viruses don't sport a lot of HP, but they attack by traveling across the battlefield in a wave-like pattern and cause Collision Damage. Naturally, their stronger forms move faster (and are harder to hit and dodge) and hit harder. Woe betide a player in a form weak to electric attacks. It is possible to forcibly alter their behaviour by causing them to orbit an obstacle, but the average player traversing the Internet is not likely to be carrying obstacle chips for this express purpose, on top of the possibility of other enemies destroying the obstacle.
- Shadow viruses are almost literally demonic (their upgrades are the Red Devil and Blue Demon). These things float idly around their territory for a few moments, glaring, and then suddenly they fly to a panel adjacent to Mega, completely ignoring boundary restrictions. While that may only sound mildly annoying, what makes them truly fearsome is the fact that they're Nigh Invulnerable. They're immune to all damage except for sword-based attacks for some reason (swords of justice cut down demons?), having their own special variety of defense. Later game virus-gauntlets love to stuff these guys in to create chokepoints for players not using swords.
- Successors to the Shadow viruses are the Navi Blacks and Shadows (Shadow-variants of Normal and Heel Navis from the fourth game), which appear in Black Earth — basically, it's a dungeon filled with mini-bosses that are immune to almost all damage. Also, the Nightmare viruses from the sixth game behave very similarly to the original Shadows, though they occupy panels in addition to their attacks, reducing Mega's dodging options.
- Protectos are defensive puzzle-viruses in the Bonus Dungeon of each game that will punish you if you fail to solve them properly. Protectos constantly count down from 10 seconds before unleashing a big explosion, and you have to defeat all of them in one shot or they will simply regenerate at full HP. Fortunately they can be stalled out with properly-timed defensive chips until you draw the combo.
- Fishy2s are this, specifically for the fire-traps they leave in your area after they zoom past that eat up one of your rows for a few seconds. You could make an argument for Fishy3s (which are essentially hyper-Fishies), but they usually show up with other Fishy viruses, and multiple Fishy viruses tend to actually negate one another's effectiveness by serving as obstacles that their fellows can't pass through, and a Fishy that can't fly is a pointless Fishy. On the other hand, you can get seriously unlucky and they will all safely launch, and woe unto you if you fight Fishy2s on a Grass Stage.
- The Null, Void, and Null&Void virus family, each with a respectable amount of HP, regenerative abilities, and the ability to summon a pair of whirlpool-traps that take 200-HP bites out of Mega's health.
- Lavagons will have a homing fire-breath attack that will leave a burning firetrap on the panels it hits. Their upgrades (the Bluegon and Yellowgon) will use similar attacks (ice-breath and lightning strikes, both homing), and these last two only appear during the SS and SSS license tests. The Yellowgon is accompanied by a pair of Hard Head 3s that will punch holes in your field, further harassing you and threatening to get you boxed in.
Battle Network 3
- Elebee viruses blip around the battlefield before dashing at Megaman. Not very deadly the first time one encounters them, but the later versions move much faster and do lots more damage, such that you only have split seconds to take down Elehornets, their strongest version.
- Number viruses are akin to Protectos in the second game. They don't actively attack at all, but they complicate the process in that you have to defeat them in a specific order — i.e. destroy all the Number 1s in one hit, then destroy all the Number 2s in one hit, then the Number 3s. Hit the wrong Number, though, and it will retaliate with a powerful "Err+Del" that can oneshot you if you're not protecting yourself.
Battle Network 4
- Bomboy in the fourth and fifth games. They stand still for a second, before creating an explosive cube and pushing it towards you. The cube can take a lot of punishment, so you'd better have obstacle-piercing chips, or thrown bombs. When the cube reaches your side of the field, it blows up after a second, and the explosion will take up every last panel. This makes AreaGrab strategies backfire as it gives the Bomboys less time to push the bombs to your side and blow it up. They also have a tendency to appear alongside other Demonic Spiders like Spidy and Cirkill, detailed below.
- This game's UnderNet is also infested with Spidy viruses - actual spiders that invade your area, not only forcing you to dance around (you have a Slasher, right?) and put you in the line of fire of everything else, but also covering your section with sticky webs that will catch and hold you for a few seconds, which will spell death in the worst sections. That, and the chip they drop is largely impractical.
- Cirkill-series viruses in have a simple programming - move in a circle around the area, and fire a shot each time they line up with Megaman. The problem comes with their speed, with level 3 versions practically lapping the area and getting 2-3 potshots on Megaman. Oh, and certain areas of the Undernet love to pair them with Spidy viruses, detailed above.
- 4 has Demonic Bosses. Once you find and beat the V2 ghost of a boss you've faced during the game, he becomes a random encounter in the area you found his ghost in... at the Omega level (that's V4 for those of you keeping score at home — they skip V3 entirely). The problem is when this interacts with 4's New Game+ system, as the random encounter rematches are possible while the player can only access first-tier Battle Chips. This leads to ridiculous potential encounters, such as GutsMan Omega during a player's first ever run-through of the Den Tournament, which would be a nightmare for new players.
Battle Network 5
- The Met3EX, a souped-up version of the common Mettaur virus. Its main problem is its ability: the shockwaves it produces turn any panel poisonous. You have about 5 seconds before you can't stand anywhere without rapidly losing Hit Points. And with 300 HP itself, you probably don't have a chip that can insta-kill one. They show up again in the sixth game as RareMet2.
- Mariner viruses are submarines that love to dive into Sea Panels (which are almost guaranteed in encounters involving them), making them immune to everything barring panel-changing attacks or electric attacks (which will strike them in that case). Their attack consists of generating an anchor in a bubble that zigzags across the field slowly, which is easy to faceplant into if the player's too busy dodging other attacks. What's more infuriating is that said bubble can block attacks, which can screw up attempts to kill other viruses. And when it pops, the anchor it releases flies straight forward and is indestructible.
- Bladias. They have the ability to erase panels you've Liberated and turn them back to Dark Panels, plus their Darkloid attack has a good range, and these don't involve actually fighting them. The first form of a Bladia has 200 HP, and that number keeps climbing throughout the game. They can block almost anything with their sword when they aren't attacking. The actual attack can crack an entire column of panels, leaving you with that much less room to move about. Let's not talk about how horrible this is when you're surrounded and at the mercy of other viruses... Players of Colonel are less screwed as KnightMan's personal Chip breaks guards and does a nice amount of damage in the process.
- Zomon are like the samurai version of Swordies, only a fair bit faster, deal two quick hits, and almost always carry invisible Area Grabs after their first few attacks miss. Hope you weren't caught right in front of them.
Battle Network 6
- The Mech virus family. Their main gimmick is to release a very weak thunder-ball type attack into your field like the Billy viruses, but if it hits you, the Mech jumps to you and immediately takes a 100-health bite out of Mega with its swords. If you think it'll be easy to dodge the ball-lightning, think again, because they usually appear (especially in the Graveyard) with Element-Dragons (whose attacks take up two columns at a time) and Fighter-planes (who pepper your entire area with bullets).