This not only protects Diancie but also protects the weaker Pokemon on the Bench
Alternatively, theres Teval, the Balanced Scale, which is more ramp-oriented and builds board presence via 2/2 creature tokens
Think of it as the MTG equivalent of the Thanos snap
All Will Be One Atraxa, Grand Unifier Capricious Hellraiser Drivnod, Carnage Dominus Elesh Norn, Mother of Machines Ichormoon Gauntlet Jace, the Perfected Mind Lukka, Bound to Ruin Mondrak, Glory Dominus Nahiri, the Unforgiving Nissa, Ascended Animist Phyrexian Obliterator Phyrexian Vindicator Solphim, Mayhem Dominus Staff of Compleation Sword of Forge and Frontier Tekuthal, Inquiry Dominus Tyrranax Rex Vraska, Betrayal's Sting Zopandrel, Hunger Dominus
Being able to simply name a card and it more or less ceasing to exist in-game was a truly amazing effect