Hi, Zyra main here!
Zyra support in low ELO is absolutely devastating. Her E snare is incredibly powerful when paired with her Q nuke and her W seeds. Even when going against a tanky team Zyra can get a huge early lead. However, she has a few serious drawbacks that require you to be very skilled with technical mechanics. The cool thing about Zyra is that you can build her as a support (Frost Queen's Claim and Sightstone) then build full AP and lose literally nothing since she comprises a large part of a teams damage.
Pros:
- High area damage
- Lots of poke
- Can lockdown enemies super hard
- Plants can block skillshots (like Blitzcrank's Rocket Grab and Morgana's Dark Binding)
- Her R, Stranglethorns, makes teamfights a walk in the park
Cons:
- Very technical. Her plants add multiple layers to her gameplay, similar to Orianna's Ball.
- Slowest movement speed in the game
- One of the lowest health stats in the game
- No escape if she's caught out
- Really crappy passive. Sure, you can net a single or even double kill if you have good aim, but it doesn't mesh with the rest of her skillset.
In short, if you're good with technical, bursty AP mages (like Syndra, Orianna, and Lissandra) then definitely pick her up.