When I first saw this card, I had to check if there was some secret wall/defender synergy going on
Of course, what is definitely not legal is trying to sell or trade them as if they were genuine cards
To help navigate that choice, consider three factors: Your land count : If youre light on mana, chances are your hand is full of spells, so playing the card for its normal cost may help you influence the board more efficiently
Apart from that, Professor of Zoomancy doesnt offer much
(Some abilities can also target unexerted cards.) But not using them has less of a direct benefit - you dont need to defend your life points, as in MTG or Yu-Gi-Oh!, so leaving cards upright is typically only worthwhile if theyre likely to be challenged by your opponent and you need them for a future turn
These creatures are just going to get outclassed very quickly