Riku of Two Reflections Since Riku of Two Reflectionss ability triggers when a creature enters, you can use cards like Thassa, Deep-Dwelling and Essence Flux to generate many copies of one card
Soul Diviner already exists, so this card adds more redundancy to the strategy, at least slotting into the same decks
Sephara, Sky's Blade is a creature who is able to reliably cut her own mana cost down to a single white mana, by simply controlling a substantial number of creatures with flying
Snapcaster Mage $38.48 Snapcaster Mage was once worth over $75 (actually, its gotten around this price three separate times over the years)
Cards like Assault Formation are a good backup plan if you're having trouble keeping your commander in play
Its a good way to fight control decks that want to protect their best threat with counterspells too