EDIT: sorry for the rant, finally I did it!!! Took forever! Was lucky he filled my screen with red bricks only. Hell On Earth spell lvl2 and he was done for...!
but!!! : the Alucard Mail is NOT in the room next to him - or at least I didn't get it! pretty sure, there are no rooms left besides the very last boss. What now?!
Edit2: still missing the two marble gallery boss ´fight.... oh my god. the last mail must be there!
The Alucard Mail is in the Marble Gallery upper right boss fight! The other two are as said!