This build is Aqua Bubble centric, if you cannot land bubbles then it will be punishing. However, the build also lets you become more proficient with bubbles because you'll be casting it much more often with an earlier cooldown.

Landing a bubble (or ulti) will be very effective because it'll deal more damage, it'll make icy ground, it'll proc imperial mandate damage and enable teammates to consume the mark for movement speed without being affected by your tidecaller's blessing.

Tidecaller's blessing will still be effective. A 15% slow and 25 magic damage is basically what Senna has right now already built into her kit. Lets also not forget our passive giving 40 movement speed to yourself and any allies hit by your spells.

Practice makes perfect!

Mental is everything, you got this!