For actual Toon decks, it is still the cleanest way to reach whatever piece the hand is missing, whether that is the Field Spell, protection, a monster, or another search route into the next play
as theres no trading aspect to MTG Arena, which is a big aspect of physical MTG, the need for wildcards becomes immediately apparent
Then you would steal the scariest threat on the table or you could take your opponent's commander, if their deck relies on it heavily, effectively neutering them until they can remove it and recast the commander
Origin of Metalbending Toph makes metal really flexible and Origin of Metalbending puts a +1/+1 counter on your board, because you know green decks love those counters
Since colorless mana is generally going to be easy to generate a fair amount of, you could get this hitting as early as turn 4 quite likely and then use it to develop a game plan
They come with a bonus promo like this Snorlax card from the Twilight Masquerade blister, and often can be found for a decent price