This is quite a powerful card for its archetype.  As a searcher, it pays for itself, and it can enable you to summon an XYZ at nearly any rank.  Especially monsters ranks 5 and up, which are usually difficult to summon for most decks.  It's advantageous, versatile and all around very helpful.  I doubt Gagaga's will be high tier, but this will at least make them good for locals.
 
3.5/5

Short and sweet today folks.  Gagaga Sister (a card that really looks like she belongs in the Madaloche family for some reason) is incredibly simple.  Not sure how such a sweet looking girl like that is a DARK Spellcaster, but I guess she's deceptive?  Her stats (at 200/800 respectively) are paltry for Level 2 even, but you'd be using her for her effect, if at all.  When Normal Summoned, you can add a Gagaga Magic/Trap card from the Deck to your Hand.  Also, you can choose a Gagaga Monster you control, and that card (along with this card) become the combined Level of the two of these cards...so you're probably looking at a couple of Level 5 or 6 Monsters, getting you a much easier Rank 5 or 6 XYZ Monster.  Have fun with that, it works well enough for Yusei.
 
Rating:  2.5/5
 
Art:  4.5/5