It's kinda disappointing that the Treasure Tree Adam is weak to fire/lightning, it makes Elbaf the opposite of Wano... it's like a paper castle, it doesn't protect anyone from anything. The WG could've just sent Akainu to negotiate with them (or destroy them) ages ago.
So, the characters who would be a huge threat to Elbaf are the following:
Akainu;
Kaido;
Big Mom;
Mars;
Sabo (post-skip);
Marco;
Sanji;
King;
Katakuri;
Ace;
Enel;
Nami (with Zeus).
The ones below would probably pose a higher danger than usual due to using fire or lightning in their attacks:
Luffy;
Zoro (Foxfire Style);
Katakuri (Yaki Mochi);
Franky;
Kin'emon;
Fossa;
Nami;
Usopp;
Draw (Vice-Admiral from Ace's novel);
Dragon #21;
Dragon #13;
Shura and Fuza;
Mr. 3;
Pearl.