So far as whether you should buy the booster box goes, I think it comes down to a couple of things
If Havi loses indestructible (probably because one or more historic cards in your graveyard left your graveyard) after having been dealt lethal damage earlier in the turn, it will die
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EXFO-JP040 Vector Scare Daemon (Vector Square Archfiend) Rating 3 DARK Cyberse Link Effect Monster 2400 ATK Link Arrows: Top-Center, Middle-Right, Bottom-Left Link Materials: 2+ Cyberse monsters (1) When this card destroys an opponents monster by battle and sends it to the Graveyard: You can Tribute 1 monster this card points to
You can pay three mana (1R, 2C) to put a -1/-1 counter on a creature you control to then deal 2 damage to a target creature or player
1 is normally all you have room for but 2 can be played in a pure build