Just a quick 'n' easy Gloom build for Yareli!
Rather than use Merulina for damage reduction and a secondary weapon-focused playstyle, we instead replace it with Gloom. This turns all of our other abilities into free healing on top of any crowd control they provide. 205% strength gives our abilities some decent starting damage, and Gloom slows enemies by 72% and all damage we deal has 10% life-steal. Keeping duration neutral and running 175% efficiency keeps Gloom as cheap as possible to sustain it as long as possible. I personally left range neutral, but if you wanted [Sacrifice] some efficiency in favor of it you'd get wider coverage with Gloom and longer grab ranges on Sea Snares and Riptide.
As for a general gameplay loop, you start with getting Gloom and Aquablades online. I pair this with an Exodia [Hunt] zaw, since Gloom's slow makes the incapacitation from Exodia [Hunt]'s pull last much longer, and the pull effect also forces enemies into range of Aquablades. As for what kind of zaw, I went with a staff. Flailing Branch's forward-block combo has a ton of east slams, meaning you can drag enemies around at your leisure. From here, how you play is up to you! Throw out Sea Snares to keep tougher enemies locked down for a bit, Slam to pull all the enemies into a pile then Riptide for lots of damage (followed by a knockdown that will take all those slowed enemies a while to [Recover] from), or just hop around slamming enemies until they die.
As for companions, I personally use a [Panzer Vulpaphyla]. The armor strip is nice, as are the viral spores. If you're running into energy issues, I'd recommend [Dethcube] and a sentinel weapon like the [Helstrum] or [Seeker] that has good spread. The [Energy Generator] precept drops orbs pretty regularly as long as the sentinel can tag enemies.