Variel: I forgot to add my rules for swimming with a somebody else, I have posted that in Rules Clarification now. You have a natural swim, and can +10 in combat giving you a 15. Which is enough to drag Kiryu at your full swim speed.
The next Grindylow swims up to stab Eko. It is Eko's turn then Kiryu. Kiryu, your hold breath is at 22/24
!roll 1d20+2? #Spear vs Eko
!roll 1d6+1 #Dmg vs Eko