Adding ingame expectations
Before any big enemy or boss is always nice that something special is about to appear.
A new Warning sign appears now.

EDIT WITH LATER UPDATE:
A bigger sign appears, (it was too small):

It is also nice to add nice titles and headings at the start of a level with a bit of good taste and style.... Instead a standard tacky message box:
PC-STEAM, 2016 VERSION:

ANDROID, 2013 VERSION:
