You can only use this effect of "Fossil Fusion" once per turn
The type got a few moves like Phantom Force, a gimped version of Shadow Force that became available for most physically oriented Ghost-types except Dusknoir, again, Trick-or-Treat, an odd signature move that makes Three types canon, and a Hex buff to make it a Venoshock clone
While there are other ways to level up, such as winning battles or using wonder picks, the most effective is opening packs
for starters, it is protected by all card effects, so the only ways to get rid of it would have to be by battle or by tributing, and even then, it can be a big threat with 2500 (a lot of monsters might be able to get over that in the metagame, but in my personal opinion, this card grouped with Hidden Magician Form can be pretty nasty to deal with because you can use it to get this card out essentially for free if you go 2nd).not to mention that every turn it stays alive, you gain a huge chunk of lps back for every monster.on the field at that time
I used Gatomon here to guarantee a KO