EDITED 11OCT (to account for Sal's changed location & learning Summoner Action Economy):
Mud & Cyntheria. Melee Turn 1.
Since Mr. Mud is a "doll," I'm assuming that Cyntheria carries him in a backpack of sorts. So until further guidance, I'll move the two of them together and assume that they are in the same space.
M&C:
Action 1: Stride SW 5 SW 15 W 20 NW 25. This should put them in square H12 having triggered no AoO.
Action 2 & 3 Act Together (2A) You and your eidolon act as one. Either you or your eidolon takes an action or activity using the same number of actions as Act Together, and the other takes a single action. So x2 Actions for Cyntheria, x1 Action for Mr. Mud
Cyntheria: Act Together (2A)
Actions 2a & 2b Strike. Fists. +8/+3 1d8+4.
NB: I roll "crits" as a reroll of damage rather than "double," that is, 1d8+4 + (1d8+4) rather than 2x(1d8+4).
Attack #1 by Cyntheria is a 23 so crits on effective AC of 13 or worse).
Attack #2 was certainly a crit. So total damage is either 21 or 33.
Mr Mud: Act Together (1A)
Mr. Mud casts Protect Companion cantrip (1A) on Cyntheria.
Ignore rolls below relating to Telekinetic Projectile. Also ignore 'flanking' in the roll text, but note that the roll values do not reflect any flanking bonus as that would apply to the target's AC, not the attack roll modifier.