Queen of the Dieing Orchid
7
EARTH
Plant/Effect
This card cannot be Special Summoned or Set. This card can only be Tribute Summoned by tribuing 2 or more Plant-Type monsters on your side of the field. Once this card is Tribute Summoned successfully, you may destroy Spell and Trap cards on your opponents side of the field, equal to the cards you tributed in order to Tribute Summon this monster. During each of your opponent's Battle Phase's, this card's ATK decreases by 2000.
ATK/2800
DEF/0500

You should change the last part to "When your opponent enters his/her Battle Phase, decrease the ATK of this card by 2000 until the end of the Battle Phase." Otherwise, the wording makes it seem permanent.

Aside from that, it seems like a card that would make Plant decks a little more fun to play. Great job.