A Spinner/DropDown that opens progressively by animationg opacity of the items.

slowdown.py

from kivy.uix.dropdown import DropDown
from kivy.app import App
from kivy.lang import Builder
from kivy.properties import NumericProperty
from kivy.animation import Animation

KV = '''
FloatLayout:
    Spinner:
        dropdown_cls: 'SlowDown'
        text: 'sing along'
        values: 'hello darkness my old friend'.split(' ')
        size_hint: None, None
        size: 100, 38
        pos_hint: {'center': (.5, .5)}
'''

class SlowDown(DropDown):
    item_delay = NumericProperty(.1)
    display_time = NumericProperty(.5)

    def open(self, widget):
        super(SlowDown, self).open(widget)

        # determine if we openned up or down
        if self.attach_to.y > self.y:
            children = reversed(self.container.children)
        else:
            children = self.container.children

        # 
        for i, w in enumerate(children):
            anim = (
                Animation(duration=i * self.item_delay)
                + Animation(opacity=1, duration=self.display_time)
            )
            w.opacity = 0
            anim.start(w)

        bar_color = self.bar_color

        def restore_bar_color(*args):
            Animation(bar_color=bar_color, d=self.display_time).start(self)

        self.bar_color = (0, 0, 0, 0)

        anim.bind(on_complete=restore_bar_color)


class SlowDownApp(App):
    def build(self):
        return Builder.load_string(KV)


if __name__ == '__main__':
    SlowDownApp().run()