Blue's ability to untap is usually accompanied by its ability to also tap (see twiddle above)
Well, Ariel, Sonic Warrior is a Floodborn character, who costs 6 Ink to play
This effect absolutely isnt worth 3 mana, especially since graveyard hate is so prevalent, even as an ETB on something else
Similarly, if you sacrifice an artifact to activate a mana ability while casting a spell with improvise, that artifact won't be on the battlefield when you pay the spell's costs, so you won't be able to tap it for improvise
I'm glad this card has only 4 defense, though
Thalia, Guardian of Thraben is great at slowing down our opponent's removal and sweepers, and since we only have a total of six noncreature spells in our main deck, it doesn't hurt us much at all