Some more feedback/suggestions I'd like to give, more centered on Merulina (but also a tiny thing to Riptide too):
1) Mobility options
Per this, it's a bit vague on what you mean - does this mean the height of uncharged Merulina jumps is being lowered? If so, then... might I suggest having Merulina mobility options available in some form? Like the ability to toggle between "Standard" Merulina mobility (which would be how I'm assuming Merulina would handle with your currently proposed/planned changes) and "Amplified" Merulina mobility (how it currently handles in the live game). I had a couple ideas on how this could be implemented:
Currently both the melee button and recasting Merulina while mounted dismisses it. It could be changed so that either recasting Merulina or pressing the melee key (one or the other, not both obviously, so you can still dismount when you wish) while riding her could toggle between the movement types - the current mobility mode could be reflected in Merulina's HP icon on the HUD (changing the graphic of Merulina, or applying some extra wave/bubble effects to the graphic when in Amplified mode)
Add a toggle button on Merulina's customisation in the Arsenal or settings menu - either of these could be combined with the above suggestion, to instead dictate whether Merulina starts in Standard of Amplified mode when summoned, so you can just set and forget instead of having to turn Merulina to your preferred mode every time you summon it
I make this suggestion because... for sure, Merulina has traversal issues in more claustrophobic tilesets (looking at you Grineer Galleon), but equally, the height and therefore distance you can cover with each jump is quite useful for traversal. Equally, bouncing around with uncharged jumps/double jumps in larger tiles and carpent bombing your foes is quite fun and feels speedy with a good sense of flow - if changes to jump height require charged jumps to reach the same heights as currently, that might be a bit of a bummer and actually make her feel worse some of the time. The option to toggle between a new tighter, more precise set of controls and the current super jumpy ones might be better than just completely reworking them.
2) Aiming Weapons on Merulina and passive synergy.
Yareli's passive is honestly not bad... however, I feel a large problem is... when you're constantly zooming around on Merulina to maintain the passive, it makes aiming pretty tough. The current best solution to this in my experience has been to use weapons that are AoE-heavy or don't require much aim, such as Akarius, Angstrum, Ocucor, Vermisplicer, Gaze, Sporelacer, and Kompressa, among others. The problem is... outside of the Kitguns, these don't have amazing Critical performance, so don't synergise amazingly with her passive. Aiming non-AoE/Autolock weapons (which most of the best crit-weapons are) on Merulina is quite hard and not very rewarding feeling - being able to go into aim mode to slow down a little helps a bit... alas, aim mode on Merulina/K-Drives is hold-to-aim only. It's especially fiddly trying to use the Tenet Diplos on Merulina as is (trying to aim while also holding down the stick to do so on a controller is not very comfortable at all)
I really think introducing the option to have Toggle Aim on K-Drives and Merulina would go partway to addressing this issue... although as many people have said, the Kompressa itself needs some change as well to make it synergise better with her, considering it's her signature weapon but synergises pretty poorly with her as is.
3) Tricks on Merulina
Simply put, there should be some kind of reward system to performing tricks on Merulina. Currently while you *can* do tricks in normal missions, there's not really much point to doing them, and adding some useful little reward to doing so would encourage more stylish play and actually trying to engage with the level for tricks rather than just zooming past everything. My current suggestions on this front would be:
Landing a trick restores X% of the total score of the trick as Health to Merulina, and Y% Health to Yareli herself - the X and Y values would have to be different obviously, as Merulina has vastly more health than Yareli does, but it may be useful to increasing Merulina's sustain in higher level content
Landing a trick adds a bonus to Merulina's armour equal to X% of the trick's score for Y seconds, also scaling with the trick's score. Performing an equal or higher scoring trick would overwrite the existing armour bonus and duration, while a lower scoring one would merely add to the armour timer.
Landing a trick applies a "Hydration" buff to Yareli and nearby allies with X meters/Affinity Range for Y duration, which would provide a small Energy or Health regen effect, like Octavia's Inspiration buff
4) A Tiny Visual Indicator to Riptide
It'd be a nice QoL to add some kind of visual indicator to the range of Riptide, even if it's just a short trim of water around the edge of the AoE, so you can gague the range of it easier on repeated castings and/or know at a glance what enemies have been grabbed by your cast and CC'd versus which haven't.