You'd probably want at least 4 songs in your discard, so you could play him for 5 ink, to feel good about it
One quick note before we started the quickest and easiest way to upgrade any of these starter decks is to buy a second copy of the starter deck that will allow us to start having 4 copies of our commons and uncommons and 2 copies of our rares and super rare to increase consistency
Meanwhile, I adore Into the Unknown. Not only is that a killer song from Frozen 2, its an excellent low-end removal tool that Sapphire/Amethyst really does need to keep up the pace, preventing foes from getting too far ahead before you have a chance to ramp up to your bigger plays
Whenever you quest with Belle Inventive Engineer you pay 1 less ink for the next item you play this turn
Tidus, Zanarkand Fayth (Thrasios, Triton Hero) Rating: 4/10 Thrasios, Triton Hero basically reads as a harder-to-cast Azure Mage
This is a good way to hopefully ensure you find a fifth mana so you'll have enough to activate Vanille's second ability, though keep in mind that the timing is a bit tricky here if you're trying to meld right away