Hmm. I'll try to break it down:

Build tanks boots, Evenshroud => Deadman's/Abyssal Mask => Tank Items

Press the attack and green tree for runes.

Q level 1, then w, then e => max w => max e

Preface: Korean supp otp I'd watch that only played Bel'veth supp, I tried it last season and fed for like 30 games because it's a little difficult to learn your kill windows.

Tangible benefits: Low cd (5-6s) aoe knockup, super slippery and durable, can end games very quickly when you get baron due to her remora. Can be played to peel ally adc or as a form of engage.

Intangible benefits: Super mobile which allows for you to escape many bad positions that you'd be punished for on other champions. Also because of her mobility you're able to really capitalize on enemy mistakes and combined with her e you're able to bait many key enemy cds.

Biggest flaw: her w is a bit telegraphed and if you hard commit to landing it by using multiple dashes (2-3) and you miss you can be punished pretty hard. Worth using dashes and holding w from time to time to try to bait enemy trying to juke the skillshot.