Astral Corruption questions

[Cor2]

I have alot of questions about Astral Corruption.

1 What exactly is safe to cast under it? Blood only?, what about mixed blood and fire or whatever?

2 What are the odds per gem spent that it will attract a horror? does hammer/ forgebonus or something like it lessen the risk?

3 Do using item rituals liek ivy crown trigger the effect?

4 What are the horrors that are attracted, just normal ones? do they scale? meaning a nastier horror for a larger spell.

thanks