During the entire movie the characters are using ice as a cooling medium. Never do you see melted ice or water indicating melted ice. This tells us this is acrylic movie ice.
When Valmora shoots Marco in the head, whoever was controlling him should have ended in a coma like Sebastian.
Simply capturing a spider should not have allowed anyone to use it without the associated technology, ie the program running in the computer and the additional devices required on the sending side of the connection including the special bath and suit. The enemy should not have been able to use the tech with only the receiver. Yet they used it to control Marco.