Every card has to go through standard for it to be legal in Modern (except Modern Horizons). If a card is only printed in a supplemental product(Commander series, Battlebond, ect.), unless a printing has appeared in a normal set, it is not legal.
June 16, 2019 11:09 p.m.
Ahh. I bought the card in a shop in a bulk box, so I was unaware of the Conspiracy set not being in standard. Thanks for the explanation!