hello, and welcome to smogon (i assume).
while it's great that you're looking to discuss a few things about NU, making new threads are meant for
thorough discussions only and would require a substantial and open-ended first post. a few examples are
here and
here.
this is an even better example for a discussion thread, because it isn't restricted to talking about one specific set that would lead to a short discussion.
if you want to post about specific sets, such as the one for tangela you're talking about, or how certain pokemon are performing in the current metagame, the
"np:" thread stickied in this subforum would probably be the best place to post stuff like this. that thread is more suited for smaller topics, such as the one you're posting about right now. if you're still confused about where you should be posting stuff, feel free to send a pm to a moderator of this subforum and they'll be glad to help you out.
however, while i'm at it, i'll just comment on the idea of an amnesia tangela in particular. frankly, it's not that good. it can boost its special defense, but offensively speaking, it doesn't really pose that much of a threat to most pokemon in return, so there are many cases where tangela will be forced to switch anyway. in addition, a +2 tangela still isn't that bulky against some of the hard-hitters that NU has to offer. for example, ludicolo can 2HKO a +2 tangela with ice beam after stealth rock while tangela can't do much in return.
252SpAtk Life Orb Ludicolo (Neutral) Ice Beam vs 252HP/0SpDef Eviolite +2 Tangela (Neutral): 42% - 50% (142 - 168 HP). Guaranteed 3HKO. 1% chance to 2HKO.
lastly, it really cuts into tangela's moveslots since it has so many support options that it wants to be running, such as leech seed. i think instead of having tangela forcing itself to stay in and set up amnesia, it should act more as a pivot that comes in to take attacks and switch out eventually, which takes better advantage of regenerator.