The Tavern

Now that it slows movement, Ozocubu's Armour is not a spell you'd want up all the time: that was the porpouse of the change. But, right now, the only way to end it is to wait for it to expire, which is inconvinient if you have it active when suddenly a situation when you'd rather have faster movement than extra AC arises. What I propose is to allow player to end it before the duration expires via an ability, like now is the case with transmutations.
I am aware that, with transmutations, it's one ability for all of them, and that evokable invisibility has "end invisibility" ability, while spell invisibility does not, and that there is probably a reason for that, and that reason could also be a reason against this, although what would tha reason be eludes me.

Its worth mentioning that slow movement doesnt work as a drawback for a skill that is used to tank attacks, not to mention 0.1 is a mediocre drawback. I often forgot that i was moving slower during ozo's effect during my recent games because of that.

Wouldn't this defeat the point of the first change? The idea was that having Ozu's came with a cost, 0.9 movement, that made it bad to always have Ozu's up. But the cost is greatly lessened if you can take a turn at any point to recover normal movement speed. The worry is that it would be best to walk around with Ozu's armour up all the time, until and unless you realize you need to move faster, at which point you can take a turn to end the ability. This could be worth it since, as dynast points out, usually 0.9 movement is not such a big problem (until you need to run, or something fast comes on screen, etc.).

(This is all assuming the 0.9 movement drawback of Ozu's as it is now actually is a big enough drawback to make it bad to perma-Ozu, which may not be true.)

If you spend a turn to end Ozocubu's Armour, then you have to move 10 times just to break even on time. Otherwise you actually slowed yourself down more than you would by not cancelling it.

I always thought that it would be more elegant to expire OA, or to greatly shorten its remaining duration, when the player took a step. Of course, there must be a reason why making OA ponderous is a better move, but that reason eludes me.

OP, as far as I can tell, "end invisibility" is there because you could end invis anyway by removing the +Inv item, and that feature is there to discourage swapping after going invisible, which is especially relevant on artefacts like the +0 mace of Sukk {+Inv}

Fair enough. Although this also seems to bring home how slight the current drawback actually is. It may not even be worth spending a turn to get rid of it, in the situations (wanting to move around a bunch) where it is supposed to matter!

just hit yourself with fire spells, clearly

I tried that, turns out you cant flame tongue yourself because its overly suicidal and i believe the same is true to any projectile spell. Fireball is ok though.

Throw flame and /flame both work. Is the amount by which the armour effect is shortened proportional to the damage done? These don't seem to be very quick ways to cancel the effect.

Throw Flame is okay as well. No clue why Flame Tongue has the "not-self" flag, but it's had that restriction ever since it was added 16 years ago (between Dungeon Crawl 3.40 and 4.00), before "spell flags" were even a thing.

Hitting yourself with a spell is a really stupid idea; but I think it should be an option on the other side of an "are you sure? Y/N" wall. I mean hitting yourself with a Phial of Floods to put out a sticky flame is generally really stupid, but if you really want to...why the hell not?

Before Flame Tongue we had Burn, and I'm pretty sure you couldn't Burn yourself either.

About the whole "hitting yourself with fire" thing: if I wanted another spell to counter the slowness, I'd learn swiftness instead.