I can confirm that the latent effect is activated under red HP,(not sure whether u need to be under 100%TP or not) and u do no need to be a mnk to have the Counterattack.
As for the spikes, it seems to be a random effect, it is not always active when u are damaged =/
Yes all Spikes stack. Havent you ever seen a Red Mage soloing this would be awsome on a Monk , Samurai , or ninja , but you wouldnt want to fight monsters that are based on the "Spikes Effect" that you have enabled on you,
Do spikes effects stack? IE, can you have shock spikes and ice spikes on at the same time? If they overwrite eachother, which one would be the one that you get with both these the other pieces of this set equiped?
i was wondering if they stacked also. my guess is since you need to be higher lvl to learn shock spikes it would be the one you get if spikes dont stack.
Not gonna state this as fact, but I don't think they stack. However, having multiple pieces with spike effects raises the probability of spikes kicking in.
Spike spells do not stack, however, spike "Effects" do. Meaning, if you have a peice of armor that gives one type of spike, and another peice that has another type of spike, then there is a chance of 1 or the other triggering. The same is true about stat weapons. The only thing to note is that they do not stack w/ the spells. Since both en spells and and spike spells proc 100% of the time, they override all other effects.