Salamu Alaikom,
In regards to the domino effect of the transfer of najasa, I read that the third mutanajjis item can no longer make other objects najis regardless if wet or dry. Does the following example apply to this: during one’s sleep, he faces semen discharging and the first object to become najis is the short he was wearing. The underwear was wet enough to transfer to the bed-sheet making it the second mutanjjis object. That had enough wetness to transfer to the bed-cover making it the third mutanajjis object. Finally, if wetness still penetrated to the mattress, does that make the mattress still tahir because the third mutanajjis cannot make other object najis?