Ok, so my final record of battle results vs. Medusa and Rahab are as follows:


Medusa
Elixir-Free Wins: 4
Losses: 4 (1 Elixir used to claim 1st Victory Reward)
Losses due to RNG: 3 (Freakin' Petrify spam... )


Rahab
Elixir-Free Wins: 6
Losses: 2 (1 Elixir used to claim 1st Victory Reward)
Losses due to RNG: 1 (Rahab got a lucky triple shot on Mordred, which prevented a full burst... RIP )

All in all, not an unexpected result, so I'm pretty satisfied with this.