They allow players to shuffle their deck, which is helpful in a variety of situations
Both sides of Valki are excellent, with Valki being hand disruption useful in the early game to steal a powerful creature (with the potential to turn into it later), while Tibalt is a great end-game card, capable of removing multiple creatures and stealing cards from your opponents' libraries to cast yourself
The main function of soulbond is this pairing, While it doesnt technically do anything on its own, each soulbond creature comes with an ability that grants something to the paired creatures
GIFTING A CARD IN COMMANDER IS (ALMOST) MEANINGLESS Yeah, I said it
You often see Legacy decks run as few as 5-6 lands that actually tap for mana and tons of fetch lands to find them
Or you can just rip out the Containment Priest and attack for two at an SCG Open near you