Everywhere is flooded. Instead of fighting normal bosses, you fight water clones of them which are more powerful. Of course, water clones suck - anyone who has fought Demyx in Kingdom Hearts knows that. Bosses seem to have damage caps, and apparently can do things like remove buffs.
There is a depth rating everywhere due to flooding. Underground = more flooded. More depth = harder.
You fight some wandering monsters which can give fishbones, which give access to a shop that has helpful items, or potions, or access to the thunder skills. You have to fight a wandering monster at depth 6 to access the skills. Outside, inside and underground areas give different skills. I think... that you must use the special skills or the correct monster will not appear.
depth 1 - 1 fishbone
depth 2 - potion + 50% initiative, 40 adv
depth 3 - 2 fishbones
depth 4 - potion - reduces item loss, 40 adv
depth 5 - 3 fishbones
For the fishbones, I like the facemask (-30ML), as it frees up some of my accessory slots. I also have the fins (enemies don't hit as much), and want to get the corset (lowers water level).
Depth 6 underground - menagerie
Depth 6 underground (with thundercloud) - inside cobb's knob, cobb's knob labs
Depth 6 inside (with personal thundercloud) - spookyraven
Depth 6 outside (with thundercloud and rain in loathing effects) - highlands, pirate cove undisguised
Oddly, my records indicate that I got a thunder thigh in the haunted bathroom. I think I was at depth 6, but not due to thundercloud, as that was the second skill I got.
depth 6, underground = tardigrade -> thunder skills
depth 6, inside, with thundercloud = aquaconda -> rain skills (I guess you need a cloud to get rain)
depth 6, outside, with thundercloud and the rain in loathing = storm cow -> lightning skills
Depth Levels: (without depth increasers/decreasers)
cobb's knob first two levels - 5
cobb's knob menagerie - 6
spookyraven - first floor 3, second floor 4
highlands - 2
pirates - 2
barr - 4
In order to get certain areas to depth 6, you have to use a skill. The progression is thunder -> rain -> lightning. By the way, make sure to remove your depth reducers if you're going for a skill item.
Getting rain skills:
So what I did was use the thunder skill Personal Thundercloud -> 100 turns
I went to the indoor zone the Haunted Bedroom, which becomes depth 6 due to the thundercloud.
fought an aquaconda
Rain skills unlocked!
Thunder - adventure in an underground area at 6 depth, get a thigh from a tardigrade
regeneration - every ~ 10 adventures, you get 30 db, or 50 db with thunder thighs.
Thunder Clap
banish for 40 turns
Thundercloud
increases depth by 2
Thunder Bird
deleveller
Thunderheart
Max HP + 100%
Thunderstrike
Stun
Thunder Down Underwear
summon underwear (disappears after rollover)
Damage Absorption +100
Maximum HP +100
Regenerate 10-20 HP per adventure
Thunder Thighs
more thunder regeneration
Rain - adventure in a depth 6 inside area (example, spookyraven 2nd floor), get a brain from an aquaconda
every 7 adventures, you get 7 raindrops.
Rain Man
noncombat, copier for monsters that are copyable that have been encountered in a Heavy Rains run.
Rainy Day
increases depth by 2
Make it Rain
+300% meat drops combat skill
Rain Dance
100 adv, +20% Item Drops from Monsters
Rainbow
prismatic damage combat skill
Rain Coat
shirt (disappears after rollover)
So-So Resistance to All Elements (+2)
+10% Item Drops from Monsters
Combat Initiative +40%
Rain Delay
passive +3 all res
Lightning - adventure in a depth 6 area, outside, fight a storm cow, drops lightning milk - recommended to use up MP to below 50 so it doesn't drain as much HP, and raise HP
Lightning Strike
insta kill, items drop
Clean-Hair Lightning
max MP + 100%
Ball Lightning
yellow ray, 100 turn cooldown
Sheet Lightning
spell damage + 100%, damages attackers
Lightning Bolt
5000 damage on 3rd use in combat
Lightning Rod
summons a staff (disappears after rollover)
Spell Damage +200%
Maximum MP +50
Regenerate 5-10 MP per adventure
Riding the Lightning
Maximum MP +100%
It seems you can keep at least one skill per ascension. It's unknown at the time how many maximum you can keep, but according to the forum, it's likely to be 3 per skill tree.
The reward is an item giving a skill that deals prismatic damage. It looks like you get an extra 1 damage per item used, which seems kinda weak? The cap is 11, so 55 damage total. I'm selling my lone beautiful rainbow.