Battle Mountain/Endless Battle

"ENDLESS BATTLE
Fight endless waves of enemies, which gradually increase in level. Hard difficulty is forced for this battle. Your highest score is recorded in your Encyclopedia's game stats section."

―Sign right next to the Endless Battle, Epic Battle Fantasy 4
The Endless Battle is an optional challenge in Epic Battle Fantasy 4. Found at the summit of Battle Mountain (one screen to the left from the shop screen, the left battle), it puts players through infinite randomly generated waves of various foes.

Wave creation algorithm

When generating a wave, the game will randomly select one of numerous formation variants. Each 5th wave is made from the hard formations pool, and all other waves are made from the easy formations pool. Formations themselves include up to 4 variables with numerous foes, out of which the game picks 1 foe per variable at random, and then builds a wave out of them, following instructions of the formation, such as which slots it should place selected foes into.

Formation example:

Foe A = Flowers, Clays
Foe B = Small Bushes
Wave = Foe A, Foe B, Foe A

In this case, both variables are consistent of foe groups only, without mentioning any specific foe directly.
The game will choose a random Flower or a random Clay for Foe A, and then a random Small Bush for Foe B, then place the result of Foe A as the first foe (slot 1, upmost one on the screen in-game) and the third foe, and the result of Foe B as the second foe. This can result in a wave of a Stunflower, a Red Bush and a Stunflower, or a Black Clay, a Green Bush and a Black Clay, or many other waves.

A more advanced example:

Foe A = Small Slimes, Clays
Foe B = Friend Dog, Mage Dog, Small Slimes
Foe C = Drill Bot, Jellies
Wave = Foe A, Foe B, Foe B, Foe C

This time it utilizes both foe groups and specific foes, with the latter being highlighted with italics in the article for better understanding.
The game chooses a random Slime or a random Clay for Foe A; a Friend Dog, a Mage Dog or a random Slime for Foe B; and a Drill Bot or a random Jelly for Foe C. It then makes a wave of Foe A's result as the first foe, Foe B's result as the second and the third foe, and Foe C's result as the fourth foe. Not too complicated.

Formations also include visual coordinates of foes on the screen. These are cut from the article for brevity, as they're not particularly interesting or informative.

Groups

A list of all groups and foes in each group.

• Bats = Blood Bat, Coal Bat, Fluffy Bat.
• Bears = Brown Bear, Chimera Bear, Undead Bear.
• Big Bushes = Big Green Bush, Big Muddy Bush.
• Big Slimes = Big Sand Slime, Big Sludge Slime, Big Snow Slime, Big Veggie Slime.
• Birds = Black Bird, Mage Bird, Thunder Bird.
• Bits = Diamond Bit, Fire Bit, Ice Bit, Thunder Bit.
• Small Bushes = Dark Bush, Green Bush, Muddy Bush, Red Bush. White Bush is not included.
• Clays = Black Clay, Blue Clay, Green Clay, Red Clay, White Clay, Yellow Clay.
• Crabs = Beach Crab, Cave Crab, Snail.
• Crystals = Blue Crystal, Red Crystal.
• Dogs = Friend Dog, Mage Dog, Tanuki Dog, Wolf Dog.
• Dragons = Black Dragon, Blue Dragon, Brown Dragon, Gold Dragon, Red Dragon.
• Elementals = Earth Elemental, Fire Elemental, Ice Elemental, Thunder Elemental, Wind Elemental.
• Eyes = Ancient Eye, Angel Eye, Frozen Eye.
• Fishes = Copper Fish, Gold Fish, Steel Fish.
• Flowers = Florn, Frose, Heasy, Rainbloom, Stunflower.
• Forts = Horse Fort, Igloo Fort.
• Golems = Drill Golem, Earth Golem, Ice Golem.
• Idols = Clay Idol, Gem Idol, Ice Idol, Obsidian Idol, Wooden Idol.
• Jellies = Blue Jelly, Green Jelly, Red Jelly, Yellow Jelly.
• Monoliths = Ancient Monolith, Sky Monolith, Undying Monolith, Viking Monolith.
• Runes = Emerald Rune, Sacred Rune.
• Runes2 = Barrier Rune, Plasma Rune.
• Small Slimes = Furry Slime, Sand Slime, Sludge Slime, Snow Slime, Veggie Slime.
• Slingers = Gunslinger, Swordslinger.
• Sprites = Flame Sprite, Frost Sprite, Lightning Sprite. Rock Sprite, Wind Sprite.
• Squids = River Squid, Toxic Squid.
• Trees = Evil Mushroom, Haunted Tree, Mad Cactus.
• Turrets = Dish Turret, Fridge Turret, Laser Turret.
• Turtles = Glacier Turtle, Lava Turtle, Leaf Turtle, Rock Turtle.
• Wasps = Black Wasp, Purple Wasp, Red Wasp, Yellow Wasp.
• Wraiths = Flame Wraith, Frost Wraith, Spark Wraith.
• Ungrouped = Cat Soldier, Drill Bot, Evil Tail, Evil Worm, Eyeball, Razor Claw, Spirit.

Easy formations

Variant 1:

Foe A = Sprites, Bits, Bats, Birds, Fishes, Slingers, Small Bushes, Idols or Jellies
Foe B = Sprites, Dogs, Runes, Jellies or Birds
Wave = Foe A, Foe B, Foe A, Foe B, Foe A

Variant 2:

Foe A = Idols, Small Bushes, Small Slimes, Crabs, Jellies, Fishes, Slingers, Birds
Foe B = Idols, Small Bushes, Wasps, Crabs, Small Slimes, Jellies, Fishes, Slingers
Wave = Foe A, Foe B, Foe A, Foe B, Foe A

Variant 3:

Foe A = Tanuki Dog, Wolf Dog, Mage Dog
Foe B = Friend Dog, Mage Dog, Crystals
Wave = Foe A, Foe A, Foe A, Foe B

Variant 4:

Foe A = Flowers, Clays, Cat Soldier, Eyeball
Foe B = Small Bushes, Small Slimes, Idols
Foe C = Big Bushes, Big Slimes, Golems, Squids
Wave = Foe A, Foe B, Foe C, Foe B, Foe A

Variant 5:

Foe A = Evil Tail, Wraiths, Bats, Clays, Birds
Foe B = Evil Worm, Bears, Clays
Foe C = Evil Worm, Bears, Clays
Foe D = Evil Tail, Wraiths, Bats, Clays, Birds
Wave = Foe A, Foe B, Foe C, Foe D

Variant 6:

Foe A = Red Wasp, Yellow Wasp, Flowers, Birds
Foe B = Black Wasp, Purple Wasp, Wolf Dog, Tanuki Dog
Wave = Foe A, Foe B, Foe A, Foe B, Foe A

Variant 7:

Foe A = Yellow Clay, Red Clay, Green Clay, Blue Clay
Foe B = Yellow Clay, Red Clay, Green Clay, Blue Clay, Black Clay, White Clay
Foe C = Clays, Monoliths
Wave = Foe A, Foe B, Foe C, Foe B, Foe A

In this case, possible foes for Foe B could've been replaced with just the Clays group, for exactly same outcome.

Variant 8:

Foe A = Mage Dog, Tanuki Dog, Wolf Dog
Foe B = Bears, Elementals
Foe C = Friend Dog, Mage Dog
Wave = Foe A, Foe B, Foe C, Foe B, Foe A

Variant 9:

Foe A = Idols, Bats, Small Bushes, Jellies
Foe B = Elementals, Turtles, turrents
Foe C = Elementals, Sprites, Turtles
Wave = Foe A, Foe B, Foe A, Foe C, Foe A

Variant 10:

Foe A = Bats, Small Slimes, Idols, Runes, Runes2
Foe B = Bats, Dogs, Turtles, Wasps, Flowers, Fishes, Slingers, Birds
Wave = Foe A, Foe B, Foe A, Foe B, Foe A

Variant 11:

Foe A = Slingers, Fishes, Drill Bot, Spirit, Razor Claw, Eyeball, Flowers
Foe B = Slingers, Fishes, Sprites, Drill Bot, Spirit, Razor Claw, Eyeball
Wave = Foe A, Foe B, Foe A, Foe B, Foe A

Variant 12:

Foe A = Cat Soldier, Small Bushes, Idols
Foe B = Forts, Big Bushes, Big Slimes
Wave = Foe A, Foe B, Foe B, Foe A

Variant 13:

Foe A = Bears, Turrets, Elementals
Foe B = Dogs, Flowers, Clays, Eyeball, Drill Bot, Jellies, Fishes, Slingers, Runes, Runes2
Wave = Foe A, Foe B, Foe A

Variant 14:

Foe A = Runes, Runes2, Clays, Birds, Fishes
Foe B = Idols, Small Slimes
Foe C = Dragons
Wave = Foe A, Foe B, Foe C, Foe B, Foe A

Variant 15:

Foe A = Elementals, Turtles, Turrets
Foe B = Elementals, Turtles, Turrets
Wave = Foe B, Foe A

Variant 16:

Foe A = Forts, Big Bushes
Foe B = Small Bushes, Cat Soldier, Drill Bot, Wraiths, Turtles, Turrets, Dogs
Wave = Foe B, Foe A

Variant 17:

Foe A = Defender, Golems, Squids
Wave = Foe A

Hard formations

Variant 1:

Foe A = Dragons
Foe B = Dragons
Foe C = Dragons
Wave = Foe A, Foe C

This one is a programmer's mistake: the game takes three random Dragons, then only places two, leaving Foe B unused.

Variant 2:

Foe A = Golems, Squids
Foe B = Golems, Squids
Wave = Foe A, Foe B, Foe A

Variant 3:

Foe A = Crystals, Dogs, Sprites, Spirit, Razor Claw
Foe B = Monoliths, Elementals
Foe C = Monoliths
Wave = Foe A, Foe B, Foe C, Foe B, Foe A

Variant 4:

Foe A = Golems, Monoliths, Squids
Foe B = Dragons
Wave = Foe B, Foe A

Variant 5:

Foe A = Elementals
Foe B = Monoliths
Foe C = Elementals, Turtles
Wave = Foe A, Foe B, Foe B, Foe A

One more mistake: picking Foe C and then not using it.

Variant 6:

Foe A = Elementals, Turtles, Turrets
Foe B = Forts, Big Bushes, Big Slimes
Wave = Foe A, Foe B, Foe A

Variant 7:

Foe A = Small Slimes, Idols, Small Bushes, Crabs, Bits
Foe B = Big Slimes
Wave = Foe A, Foe B, Foe B, Foe A

Difficulty

Main article: Difficulty#Epic Battle Fantasy 4

The sign that states Endless Battle runs on Hard difficulty is not true. Stat-wise, it is in fact closest to Hard, but with certain perks. In Endless Battle, foes have the same offensive stats multiplier as on Hard, but a lower health multiplier (1x vs 1.1x on Hard), and have their evade decreased by 10%. Slimifying attacks' status infliction chance and Mana Drain's amount of mana drained would depend on your difficulty chosen in Options and isn't affected by Endless Battle at all. So would players' Limit Break charge rate, as it depends on the difficulty not only by modifying foes' damage, but also by using a difficulty-specific multiplier for charge rate itself — the former is fixed in Endless Battle, while the latter is not affected by it.

In short, if you're looking for acquiring Endless Battle-related Medals the easiest way possible, switch the difficulty to Easy before starting it. That'd make slimifying attacks and Mana Drain slightly less dangerous, and Limit Break gauge would fill slightly faster. Of course, if you wanted a pinch more challenge, you could try it on Epic to have more powerful Mana Drain effects and an even slower Limit Break gauge.