While working on Return to Ravnica design, I came up with the populate mechanic
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The effect of the hand cost is a draw, and if you use this card as a cost in the middle of leveling up, there is a risk that the cost for leveling up will be interrupted, so basically when you raise LV7 to LV10, you want to use it as a cost
Oko is in the same color combination as Hydroid Krasis, a card which excels in ramp decks, paying you off with more cards, more life, and a huge flying, trampling body
Finally, I also took the time to introduce a new non-Tuner to the mix, Red Lotus King, Flame Crime (YGOrg Translation) , as it synergizes with Fiend Tuners, as well as sending a Normal Trap to the GY when used as Synchro Material