These cards have held their value pretty well, unsurprisingly
In a recent Good Morning Magic video, designer Chris Mooney says there was always a plan to create more My Little Pony cards, as you can see from Twilight Sparkle's ability, referencing pony cards that had not yet been released
Other mobilize cards also turn into great card draw, but there are lots of effects in the wheelhouse of Mardu's color combination that bring in temporary attacking tokens like Fire Navy Trebuchet, Urabrask's Forge, and white does away with the temporary nature altogether on Adeline, Resplendent Cathar
WotC found Breach, especially with Mox Opal, made for a combo deck that was too fast, resilient, and non-interactive, even winning on turn one
I literally just started learning about Pokemon cards and ran into the topic without knowing it existed many times