If either the opponent or the permanent you control becomes an illegal target by the time Iroh's second ability resolves, the ability does nothing and you cannot choose to have the opponent gain control of the permanent
Constructed matches follow a number of individual formats, including Standard, in which cards from a defined number of recent expansions are allowed
In the mentioned scenario, our board is always the same, because we have none
[28] The illustrator, Yu Nagaba, made similar cards for Eevee and the other Eeveelutions, which are equally funny
It seems unlikely that $120 will be the new benchmark for this card
Copied creatures do have summoning sickness because they entered the battlefield on that turn