If an effect causes Purphoros to lose all abilities, its ability that causes it to stop being a creature still applies if appropriate
The way challenging works is a ready (untapped) character exerts and chooses an opposing exerted character to challenge, and then both cards compare their strength (attack) and willpower (defense) values to each other (meaning the attacker automatically gets hit back by the defender)
That effect naturally creates powerful combos with cards like Ob Nixilis, Unshackled and Opposition Agent, along with anything that punishes opponents for searching their libraries
Start with small stakes while exploring new titles, and track your results to understand variance over time
Sorry it's not hitting the seventh spot...but that would be rough to sell...amiright
I know that [[Miirym, Sentinel Wyrm]] has already spiked in price