When Silent Hallcreeper becomes a copy of the target creature, it's neither entering nor leaving the battlefield
Spoiler: If you pull a manga Mihawk, retire early
Start with Buggy or Luffy first
Part of its appeal lies in the fact that its from this set as it was a set which was never reprinted after its original print run, making the task of obtaining even one copy of this card much more difficult than it would be for just about any other card
However, the 1-kill performance has improved, so if you use a lot of support, you can do something about it, so why not try using it
Ultra Deck 9 12 [27833] JP096 Triple Tactics Thrust Normal Spell If your opponent has activated a monster effect during this turn: Set 1 Normal Spell/Trap directly from your Deck, except "Triple Tactics Thrust", or if your opponent controls a monster, you can add it to your hand instead