In order to count toward Juggletron's power bonus, a sticker must be completely within Juggletron's art, such that no part of the sticker is touching the frame, another sticker, or Juggletron itself. This includes the entire sticker, including the white border.

Additionally, the stickers must depict tangible items, so sound effects, thought bubbles, and the like won't count.

If you put name, ability, or power and toughness stickers in Juggletron's art, they'll do what they're supposed to do as stickers, but they aren't items Juggletron can juggle.

Counters are also items that Juggletron can't juggle. They're not part of the art, and Juggletron just can't get a grasp on them.