Cascadia Flare

A maxed out flare will not do much for the base hit, but does provide good damage for the explosion. It also provides much higher heat proc damage.

A comparison between stacked flare and empowered:

• Flare 480%
  2 x 4.8 + 168 x 4.8 = 9.6 + 806.4 = 816
• Empowered
  750 x 2 x 0.3 + 2 + 168 = 620

Riven

This weapon scales well on multishot, and is a lot more fun as you get more bubbles. Heat helps to stack bigger heat procs, and damage is reasonably helpful even though a full Flare gives a lot. Crit stats are pretty useless.

X Shot

[Galvanized Shot] doesn't work on the AoE. Considering the AoE is over 95% of the damage, if you are getting 360% damage bonus from [Galvanized Shot], your marginal DPS gain is only 8%. Plenty of other stuff gives more damage.

Standard Multishot Mods

Any [Barrel Diffusion] will work. With Amalgam providing an absurd speed boost if you are good at movement, or Galvanized providing ~27% better DPS compared to Amalgam. And of course [Lethal Torrent] for both single shot and sustained DPS.

Auger Pact

Hornet Strike is strictly better for damage, but a loss of 15% DPS is worth the utility of Pact for me.

Triple 60-60 Elemental-Status Mods

These help keep most of the elemental damage balanced towards heat, and provide the status chance to gain a good number of heat procs.

Exilus

[Lethal Momentum] +40% projectile speed means +40% travel distance for your bubbles on top of easier shot leading. Though if you plan to use the weapon constantly, you may need an Ammo Mutation Mod Instead