When you use tangrowth you really shouldnt worry about burns unless you are a physical variant. Regenerator shouldn't be underestimated, it heals a lot of hp and you can continuously just bring it back in on double downs and immediately switch out to get some more hp. Over the course of the match, the burn damage will be pretty insignificant if you're using it to check bulky waters. I would be more worried about taking u-turns than bulky waters with Tangrowth.
Aside from the Jellicent suggestions, a ferrothorn will be able to somewhat handle scizor. CB u-turn is not a 2hko on 252 hp variants and you can make that a 3hko if you invest some defensive eVs into it. If you want to handle Scizor better you can go with Rocky Helmet, but you can also use the chesto resto set to handle bulky water burns a bit better.
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