The dog dragon skillup dungeons are BS. I ran wood and dark countless times, even spent a stone for a refresh last night that net me zero skillups. I was trying to skill Avalon Drake and Akechi, wound up 3 short of maxing Avalon drake and didn't get any Akechi skillups. I thought by now they'd be improving the skillup system, not making it worse. Those Akechi skillups were so completely rare and even when they did show up it was a one in four chance.
Bolded lines are an objectively correct answer.
Sadly, most have not realized that GungHo snuck in quite a few nerfs with the move to 3 minute stamina.
Fun Fact: (Newer skillup dungeons cost MORE stamina per boss drop at 3 min stamina than older dungeons at 5 min stamina)
Pre-Nerf Dungeons (Up to Cat Dragons) - Guaranteed drop at 50 stamina each.
Post-Nerf Dungeons (Armored Dragons and beyond) - Long-term average drop at 100 stamina.
Stamina regen increased by 67% per day, moving from 5 minutes to 3 minutes per point.
Net boss drop stamina cost increased by 100%, as dungeons moved to a two-boss format.
** In-line drops can't really be objectively nailed down, as no one really knows the spawn rate per floor, per difficulty. Subjective evidence implies that higher difficulties equals a higher spawn rate. But even so, only 1 rare spawn can appear per floor, which often places it at a 1 in 4 or 5 chance of dropping (and may not even drop at all, unless on 2x drop rate, unlike boss floors on mythical difficulty).
Coupled with tricks such as:
-- Fewer trash floors to actually spawn said rare skillup mobs (see dog dragons, which only have 3 possible floors for a dog to spawn on in a 7 floor dungeon)
-- Restricting rare skillup mobs from appearing **at all** on lower difficulty levels to prevent players from obtaining said skillup mobs from mass running cheaper versions a dungeon (see Gears in Armored Dragon, where R/G/B gears require 25 sta min for a chance to appear and 40 sta for L/D gears)
The drop rates are intentionally extremely low, and will be forever and ever until said skillup mobs are "voted" into the survey carnivals (likely at the point in which the relevant gods are out of the meta).
Funny thought about that.... as more and more skillup mobs get added to the survey carnivals pools (and they eventually will), the appearance rates for each mob get lower and lower and lower.....