Oh, right, yeah the Arnassi costume does something too, I just NEVER use it.
It makes you go twice as fast on a seahorse. I've just tested it out over a long piece of track, and without it took 5 seconds and with it almost took 3 seconds, so I'd say it's a bit less than twice as fast. You can definitely notice this when on a seahorse with the costume, because you swim faster than in fish form.
Er, after going through a script there is a value of 3.5 when not wearing the costume and 5.5 when you ARE wearing the costume, I was pretty close.
On the crab + defence, I tried the same thing as last time. I used Chomper, the big orange piranha that looks where you are, then suddenly dashes towards you.
He normally damages you with exactly 3.2. (in script)
With only Crab armour he damages me less than 2.5. (I let him attack me twice, I was still alive)
This means that the multiplier is in fact not 1.25, but 1.3 or higher.
3.2/1.25=2.56, 2 hits of those and I'd be dead.
3.2/1.3=~2.46, 2 hits of these and I'm alive.
3.2/1.4=~2.29, 2 hits of this and I'd have half a health left, which I really didn't, as so, 1.3 it is, seeing I don't think Alec would take weird random comma numbers.
And with Crab armour and plump perogi +2 defence put me up with less than 1.25 damage. (after 4 hits I was still alive.)
With only the +2 Defence he got about a third of my health, after 3 hits I was still alive, so I'd say exactly 1.6 damage
We can conclude from this that the +2 defence halves the damage you gets. 2x defence multiplier.
And also that crab armour still keeps your defence. 1.3 multiplier.
I also think that the food first halves the damage, and then the multiplier of the crab armour, not both added together.
I haven't tried food with +1 defence, but I suppose that's a 1.5 defence multiplier.