Ivern's playstyle as an ADC is somewhat flexible, but by far his easiest lanes are the ones where you can play aggressively.
Why are these champions good with Ivern?
There's generally 3 types of supports that go well with Ivern ADC:
Engage supports that can deliver Ivern's shield
Engage supports are the most straightforward to play with. Not only can they deliver Ivern's 70% slow from the shield explosion, but they also have good synergy with Ivern's Q dash. For example, Alistar can take Ivern's Q dash, use his Q, and then headbutt them back (like the aram snowball combo).
Ivern's DPS with W autos is at a similar level to regular adcs early on, so as long as the engage is solid it will lead to a kill.
Champions who can follow up Ivern's slow
While champions like Nami and Seraphine can't deliver Ivern's shield themselves, they have great followup on the slow. In these lanes, let Ivern engage with Q+E and combo Nami Q, Seraphine E, or Brand W on top of the slow.
These lanes do have kill threat, but they heavily rely on Ivern landing Q. Losing control of the wave is also a big problem here, so it's important that the support attacks the wave when necessary.
Non-support bruiser/fighter champions with high base damage
Since they have high base damage, the only reason why champions like Rek'sai and Rumble can't function as supports is because they need a good way to both gap-close and lock down a target. Ivern can achieve both of these for them with his Q and E.
There's a few very bad matchups for Ivern/Bruiser lanes (such as heavy disengage or high range), but otherwise this type of lane is free.
For roaming and scaling support champions
Although playing the Ivern lane aggressively is preferred, sometimes the support has a limited champ pool, wincon is mid/top, enemy team forces vertical jg, etc. In these situations, Ivern is able to play safe and scale due to being difficult to dive and being functional without gold.
Ivern can also be run in hard-scaling lanes like Ivern/Sona or Ivern/Soraka, but he's a lot easier to punish than a champion like Seraphine due to his lack of range and waveclear
tl;dr: weakside Ivern with roaming/scaling support isn't optimal, but it can be made to work if needed.
Since I haven't experimented with everything on Ivern ADC yet (I have about 200 games of it atm), many of the tier list placements are made by assumption and could be incorrect. I'm gonna be labbing ADC throughout the preseason, so for now the tier list is very subject to change.
My goal is to figure out a way to play with any support and win lane by searching for all unexpected synergies/tech. It admittedly isn't a very realistic goal, but let's see how close I can get!