1 Tuner + 1 or more non-Tuner monsters Once per turn: You can banish 1 Plant-Type monster from your Graveyard, then target 1 face-up monster your opponent controls; halve that target's ATK, until the end of this turn. During the Battle Phase, if this card attacked: You can banish 1 Plant-Type monster in your Graveyard; halve this card's ATK until the end of this turn, and if you do, this card can make a second attack during this Battle Phase.
The attack boost given by Metalmorph scales with the monster you battle, so Splendid Rose can still beat its opponent even with her attack halved.
You can summon Splendid Rose by combining your Special Summoned Aromage Marjoram and Aromaseraphy Angelica. Aromage decks don’t have much interaction with the graveyard so Splendid Rose can banish as much as she want for effect cost.