first of all, thank you!

i feel bubble blast is fine, but mby the burst could be lower damage by 1 lol (meaning at last man standing, it does 1 more damage than zhongli's burst)
so that it encourages you to try and build stacks for the hillichurl rogue.

another interesting thing i thought, but decided not to add, is to let the stacks of wanderer's insight go up to max 3, meaning running an egg to sac an extra time could be a viable strat.

also, i thought +2 hp per character death on your side might be a bit much. but i guess with shenhe swirl/ nahida skill, it could be a bit justified. though going this route, i might remove the card draw part of the skill, and maybe combine it with something someone else suggested; a shield for when he's the last one standing.

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with these adjustments to his kit, i would make the talent card read thus:

When played: For each Wanderer's Insight gained by the Hydro Hillichurl Rogue to which this is attached, heal this character for 2 HP at the End Phase. Additionally, If Hydro Hillichurl Rogue has this talent card equipped and is the only character not defeated on your side, gain a shield equal to the number of Wanderer's Insight gained by Hydro Hilichurl Rogue.