I was playing the Tarum solo mission (Shara quest pack) and played an Apex Predator on Tarum’s (Oakling) buffed Wood Elemental (see picture below). Some visula effects (I think the faeria cost reduction effect) occured on each of my cards when I placed Apex below the Elemental but I did not see any changes to the cards’ costs. I then selected the elemental for the Apex buff and Apex dissapeared/exploded/died and all my creature cards’ costs increased by three (see picture).
If I remember correctly this occured after a card of mine got destroyed at the start of my turn because I had too many cards. This was really funny and not so funny at the same time 
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(edit: additional information)
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