The beasts may challenge our gods

This is part of a GLOG community project to make rules for fighting and playing as kaiju (if you can believe it), proposed by Arkos over at Tome of Dreams. Some parts were quite a challenge, but it's the kind of challenge that you really want to rise up to, and I can only hope that I did a good job.

Skullcrawler by Dope Pope

Titans: gargantuan forms of incredible power. Easily as large as two houses, more powerful than any human but slow in their enormity. Titans have titanic vigor and deal 1d6 titanic damage with their attacks, each of which is six times normal vigor or damage. Normal damage is not counted against a titan unless a single attack deals more than six damage, but both the titan and their human-scale opponent hit automatically. Making equipment or items for titans is impossible outside of a large city or somewhere with similar manufacturing potential, and all items cost 100 times as much money. Titans move along titan tiles, each of which is 30 meters square, but can only act on every third round in combat.

Titan suits: what we might think of as 'mecha,' each needs a human crew piloting it in order to fight effectively. At minimum a pilot is required, but works best along with a gunner and engineer, often with room for secondary pilots, gunners, and engineers as needed. Each pilot can spend their turn either moving or turning, and gunners can only target enemies roughly in front of the suit. When titanic weapons are fired, the gunners must spend a turn reloading them, unless they have a secondary gunner to reload immediately as they fire, and each weapon requires gunners manning it. Engineers can field repair damaged systems, one per round. After the battle, vigor and system damage must be repaired properly for 25 gold each.

quasi medieval wooden mech by Lukasz Dudasz

Kaiju: independent titanic monsters. They must seek out huge quantities of food at a relatively slow rate thanks to their large, slow metabolism. They only need food once a week, but are sated by no less than 100 times what a human would eat in a day (generally 20 gold worth of food, or another giant monster). In melee combat against another kaiju they must use combat stances.

Kaiju

Each level requires 10 times the normal amount of exp
Stat bonus: +1 maximum Megaton

Starting skill: builder, climber, or survivalist

Level 1: a titanic monster!, only one thing can stop it!
Level 2: it's heading towards..., there on its back!
Level 3: its mouth is opening...
Level 4: strangest of all..., it's so... powerful!

A titanic monster!: your huge body has titanic vigor, and your claws, teeth, enormous fists, a casually lifted vehicle, or however else you choose to attack, deals 1d6 titanic damage.

Only one thing can stop it!: the sight of your weakness will halt you in your tracks, allowing only an attack or movement per turn while it is near. If it can damage you, take an extra die of damage.

1. Fire
2. Water
3. Beauty
4. Daylight
5. Blood
6. Wood

There on its back!: choose a set of limbs or protrusions, adding new mobility options. 

1. Expansive wings: they unfurl like the sails of a massive ship, blotting out the sun as they carry you beyond the earthly plane.
2. Myriad legs: pulling aside dirt or sand, allowing you to travel underground through any soft earth.
3. Translucent fins: along with gills, allowing you to travel freely underwater.
4. Loping arms: bending down around your body, able to propel you twice as fast as other titans.
5. Gelatinous bones: compress your body down to fit through any space two horses could fit in. While compressed you cannot fight properly.
6. Shimmering eggsac: consume one Megaton to place eggs where you are. They have 1 titanic vigor, but as long as they aren't destroyed and you don't place new eggs elsewhere, you can evaporate into dust, hatching fully formed from the eggs in an instant.

Squid Kaiju Baby by Roger Gerzner

It's heading towards...: determine what source will power your preternatural might. Each time you find a great enough source, gain one Megaton. You can spend your turn to consume one Megaton and heal 1d6 of your titanic vigor.

1. Magical energy: a legendary artifact or order of lesser mages.
2. Lightning: a lightning bolt, or an alchemical engine like unto a modern power plant.
3. Heat: a few blacksmith forges or a flow of lava.
4. The adoration of children: spend a day catering to a group of children.
5. Blood: a village worth of people, or a herd of large animals.
6. Gold: 60 gold coins, or two kilograms of gold.

Its mouth is opening...: consume one Megaton to use a breath attack on your turn.

1. Incendiary tongue: heat like the fires of hell blast from your maw, spilling out into a cone up to 90 meters away, dealing 2d6 titanic damage.
2. Hyperborean breath: your exhalations frost over all before you, up to 60 meters away, dealing 1d6 titanic damage. Anything that would be killed by this damage is instead magically frozen, protected by ice unless shattered or thawed. 
3. Voice of the storm: a bolt of lightning cracks forth from your throat, darting into one target of any size up to 120 meters away for 2d6 titanic damage.
4. Venomous belch: cough noxious clouds over the puny creatures below, filling a 90 meter square area centered around you with poisonous gas for 1d6 rounds, dealing 1 titanic damage to anything in it each round except yourself.
5. Crystal seed teeth: gnash and spit teeth about, sprouting great crystal trees that impede and fill up to three tiles adjacent to you.
6. Frenzy brood: spit out tiny young, 1d6 monsters with 1 titanic vigor each, which deal 1 titanic damage with their attacks. They are as small as horses, and will die after 6 times 1d6 rounds.

Godzilla vs Kong fan art - Nuclear Breath by Jonathan Opgenhaffen

Strangest of all...: select one final mutation, either from the list below or from either previous list.

1. Immortal conception: a week after being killed, consume all Megatons to give birth to an infant kaiju who is helpless for a month. It can move and eat if food is provided for it, and after the month it will grow back to its previous size, one level lower. Each Megaton absorbed in this state hastens maturation by a week.
2. Axe scales: anything touching your skin takes 1 titanic damage.
3. Living mountain: consume one Megaton to wreathe your body in impenetrable stone, gaining +3 titanic defense for ten rounds. Normal sized attacks will be unable to damage you at all during this time.
4. Lifebringer: consume one Megaton to send out a cloud of healing spores, healing every living thing within 100 meters for 1 titanic vigor.
5. Neural link: take a weapon or limb from a defeated titan and attach it to your body. It will last for 1d6 days or unless destroyed in some other way, and you can use it as freely as the original host could.
6. Explosive growth: consume one Megaton to double in size for 1d6 rounds. While in this state, you occupy an extra tile and deal +2 titanic damage with normal attacks.

It's so... powerful!: consume one Megaton before picking a combat stance. If this attack hits, it will deal 3d6 titanic damage.

Enemy Kaiju

Night of Silk
A circus once used tents inhabited by spirits to make their travel easier. They brought on more of these spirits, easing their way and filling the nights with whimsical shows of floating lanterns, dancing dresses, and nervous but exotic beasts. The spirits started to collect more spirits, more tents and decorations that could dance with them, until they had swallowed up their mortal stewards and drifted into the sky, captivating one audience after another.

Shirintu the Blight
A dragon captured by a wartorn kingdom. She was cursed, mutated, and enchanted to create the ultimate war beast, but inevitably shattered her bonds and destroyed her longtime tormentors. Her breath is cursed green flame flecked with shards of red glass, and her body is speckled with venomous pustules and red needles.

Grulputh
A god of goblins, or godlin. It is a gibbering, spaztic, conniving coward, and it is taller than a windmill. Somehow this sickly green menace always manages to hide its huge body, and sees fit to rob peasants and leave huge traps hidden in the woods.

Other participants

Arkos at Tome of Dreams: https://tomeofdreams.blogspot.com/2020/03/kaiju-challenge-gigantes.html?m=1
The Byzantine at Espharel: https://espharel.blogspot.com/2020/02/osr-kaiju-rules-and-class-kaijui-barely.html
deus ex parabola at Numbers Aren't Real: https://as-they-must.blogspot.com/2020/02/giant-monster-i-hardly-know-ster-glog.html
Lexi at A Blasted, Cratered Land: https://crateredland.blogspot.com/2020/03/giant-robots-deserve-giant-monsters.html