Haven of the Harvest itself isn't amazing, but it's a strong option on the backside of Strength of the Harvest, and Urza's Saga isn't one you'd think to run with an enchantment commander, but it is an enchantment land that has unrivaled utility if you can afford it
Mana Drain does benefit from complementary deck design which is basically useful ways to expend an influx of colourless mana but beyond this it is very good in any kind of deck
(Plus Merlin, Shapeshifter in his own human form.) Each of the shapeshifting Merlin cards offers a different boon when they first arrive on the table and when they leave, presenting the opportunity to combine them with cards that cycle them in and out of your hand to stack up the benefits
The Elder Dragon is played in a variety of Commander decks, like the other Elder Dragons, and is the least valuable dragon from the CLB cycle
Broken Bond should be considered in the utility slot for any deck that cares about making extra land drops