Then you can attach as much Water Energy as you have heads
A 5/5 Cat Nightmare Beast with deathtouch and lifelink for five mana, whenever Nethroi mutates, you can return any number of creature cards with a total power of 10 or less from your graveyard to the battlefield
If you've already got a lot of cards from The First Chapter, apart from the guaranteed foils in the 2 decks, it might be more cost-effective to put your money towards boosters, unless you're looking to pick up the cards from either of the starter sets quickly, then the fixed nature of the decks will get you those quicker than randomized boosters
2/2 Human Knights with trample and haste are quite good to make, and if they can crash in and deal damage, you even get to snag the monarch for yourself a turn
Use a binder with pocket sleeves
If heads, shuffle Masters Key into your deck. A grade 9 sold for $26,900 at auction in August 2020