Giving all your dragons indestructible means you can swing and block without fear, and the bonus of stacking +1/+1 counters every upkeep quickly snowballs, all on top of a potential alternate win condition
Mind Twist Targeted discard takes a huge hit in Commander compared to Constructed formats, since it typically only interacts with one opponent and doesnt affect the board
I have a soft spot for creatures like Figure of Fable, which can be cast as early as turn one, and can be leveled up by paying mana into its activated ability
Just like how Niv-Mizzet counts two colors, use multi-colored lands to smooth out our mana base
As a player who cares primarily about Underground Sea as a game piece rather than as an investment, a few dings, scratches, or an artist's signature probably aren't a big concern