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
Yes, rarity matters, but a card's financial value is driven by two things: collectability and playability
High-grade Alpha cards are already rare due to the lack of protective sleeves in Magics early days, and finding one in pristine condition is nearly impossible
Iroh, Tea Master Next up is this fun three-drop Boros rare legendary leader
It has a lot of partner commanders, which allow you to have two commanders instead of one
The car gives itself +1/+1 counters for each even result you roll and for each odd result you roll, you get an adorable 1/1 white Clown Robot artifact creature token