My thought process is that if you are already playing four Ally Gideon, Gideon of the Trials makes a fine one- or two-of to pair with him
This rainbow foil version of the card is extremely rare and desired for the same reasons as the non-foil version but now with added flair in the beautiful holo on top of the stunning art
A surprising amount of card draw can help keep your hand full, while flooding the board with tons of creatures
So, if you've dropped an Impervious Greatwurm or Krosan Cloudscraper this turn, you can immediately double its power and attack with it for devastating damage
A 3/3 for three mana with Toxic 1 is already a reasonable deal, but considering that achieving Corrupted is likely going to be a goal of many Phyrexia: All Will Be One draft decks, the upside here is tremendous
The only way it'll work for you consistently is by playing it on your own creatures, but you can find better options