Thunder doesn't have debuffs at the moment. Just Raiko for A frame Atk and Tyr for A frame Def. That'll be fixed in early March with the release of Mardook for C frame Atk and early May with the release of Mammon for C frame Def.

Thunder still has some problems, though. Namely, Mammon has HEAVY synergy with Dartagnan, so you're going to want to use her for Snatch and B frame debuffs. However, that leaves you entirely without heals or other tools. Thunder in general lacks tools, unlike elements like Water where just about every SSR has multiple ones.