Ethereal Investigator As I mentioned in my Type Four conversations online about including this card in our Type Four stack where investigate cards can be paid immediately, "This is better the more players you have." I mean we run cards like Mulldrifter (which is also free if you evoke it), Cloudblazer, Sphinx of Uthuun, and Sphinx of Enlightenment for card flow from a dork, but if you are running around too many duels, then this is essentially a mana 2/3 flyer that replaces itself and makes 1/1 Spirits with flying on your 2nd card drawn each turn, so one with the Clue after you sac it
The card does, additionally, synergize with Jin Sakai, Ghost of Tsushima, the focus of this Secret Lair drop, potentially allowing Jin Sakai to give Double Strike to other unblockable creatures for massive damage
al., but also the newly-reprinted Cavern of Souls, plus Mutavault as a free bonus merfolk
Good Condition
As long as you have enough non-land mana sources to produce two mana each loop, like artifact 'mana rocks' such as Sol Ring or mana dork creatures, you're golden