Their trigger reads, Whenever a land enters the battlefield under your control, you may gain control of target creature for as long as you control Roil Elemental. So, basically, as long as you can keep Roil Elemental alive, you can absolutely steal every other Creature on the battlefield
For example, Jace the Mind Sculptor, is $40
Enabling High-Cost Spells: Blue ramp cards allow you to cast high-cost spells earlier in the game, catching opponents off guard
Its somewhat useless in the Merfolk deck with plenty of better options, but in a dedicated Wizards deck, it provides quick ramp into your best spells and a Wizard on the battlefield for Wizards Lightning and Wizards Retort
I see her fairing better in the long run, however, than the location/song cards on this list given her status at Disney Princess
This makes all of your Rats much better in combat, forcing your opponents to trade their creatures if they want to block a Rat, which will then give you more Rat tokens as another creature dies.
