Water
Water is a terrain type introduced in No Heroes Allowed! that allows for aquatic monsters to be spawned. It can be accessed through poking geyser blocks while digging out the dungeon. This opens up numerous strategies for the player and can allow for many unique dungeon structures. Normally, three geyser blocks will be available on any one playthrough of a chapter.
Overview
When poked, a geyser block will spew out copious amounts of water into the general vicinity. It will always flow downwards, and when it comes into contact with a horizontal space, it will spread evenly in both directions. It is the God of Destruction's responsibility to flow the water into an optimal position. Monsters contained in the water will follow the water unless they're at the peak of the flow, in which they may get left behind. This flow can be used in a variety of ways, such as an organised assault on a hero, moving it to find new nutrient and mana sources, and more. However, water can never flow upwards, so any time where it flows downwards, it cannot be brought back up through any means.
Water gives rise to many monsters once it settles in an area, so long as nutrients and mana are available in adjacent blocks. Thus, it is optimal to have as much water adjacent to nutrient- or mana-rich blocks as possible. In the event these conditions are met, mould will spawn on the blocks and begin absorbing the respective nutrients and mana before sprouting into a Lily Bud and landing in the water. From here-on, it can be poked to spawn as an Aquachnid or Thunderhead respectively. However, it can be left alone to grow to spawn Hurtles or Loreleis, or into a Water Lily to raise Dungeon IQ. Because monsters will randomly spawn on their own, water areas are almost completely automatic and require little maintenance outside of regular culling to ensure nutrients and mana remain distributed.
Fossils can be soaked with water to spawn monster such as the Not So Blue Whale or Wandering King to further diversify the lakes, allowing for slightly more variety in monster lineup.
Water monsters tend to be more defensive in nature to match how water itself slows heroes down a bit. Aquachnids spray webs onto heroes to further slow them down, Thunderheads obscure their vision and cause them to miss, Hurtles can block their path and throw hammers at them, and Loreleis can electrocute them to stun them momentarily. The Not-So-Blue Whale can also use its special ability to heal water monsters throughout the ordeal. Thus, long, waterlogged corridors are excellent death traps for Swordsman- and Warrior-type heroes, overwhelming them through sheer numbers and "annoying" strategies. This is further rewarded in respect to the Aquachnid, which will spawn an Aristoquachnid if it fells a hero akin to an Omnom.
Monsters not native to water will lose HP more quickly, as if they are drowning. Due to this issue, if bringing a body of water to a new location, care should be taken to not soak the land-based monsters, lest they get stuck and die. Monsters will quickly attempt to leave water should they enter by accident. Likewise, aquatic monsters that leave the water will quickly try to re-enter, and will dehydrate and die if left out for too long.
Alchemists, Priests, Magicians, and some Iron Men can freeze water using magic, which will freeze all the water monsters within as well as any other monsters that touch it. They can be broken free through using the pickaxe, but only momentarily; it does little to make up for the damage. Water monsters will be treated as if they were on land for the duration of the effect too, rapidly losing HP.
Shamans can spawn holy water to try and counter water monsters, in which entire bodies of water that come into contact with it will be purified. Additionally, if the flow leads the water out of a corridor, it will move the entire body of water along with it. Worse still, all regular monsters that come in contact with the water will become weak, feedble, infertile Pure Breeds, such as Pure Dragons. However, once the offending Shaman is defeated, the water will become stagnant again, in which it can be used for more elaborate water-based strategies thanks to the increased amount of it.