Hadesa

Lady Valena Toland tells Princess Arianne Martell that there are tales of krakens off the Broken Arm, pulling under crippled galleys. Valena says their maester claims that the blood draws them to the surface. She adds that there are bodies which remain in the water, while a few have washed up on Ghost Hill's shores. Euron will use priests to summon krakens

If valyrian armor is fireproof it makes sense in some way. we can assume that armor was more rare than dragon because of fireproof and armor was only strongest valyrian dragon lords privilege. armor was advantage for them if it would come to dragon battle against a dragon raider who did not had an such armor. Also explains why targs didn't had one