I just felt like keeping this lighthearted a little, but this is worth pointing out.
The Octomammoth battle is pretty straight forward as you don't have that many choices to go on..
But did you know that cute Chocobo is stronger than whatever Tellah has as an option? For 2 MP more, it might just be w0rth it.
Lit1 has a base spell power of 16.
Chocobo has a base spell power of 40.
Octomammoth has a magic defense of 25.
Tellah has a natural spell mutliplier of 5 (16 Wisdom / 4 + 1), Rydia at level 12 has the same amount.
Since lightning is effective against Octomammoth... this means...
16 (spell power) * 2 (weakness) * 1 (worst case scenario) - 25 = 7 * 5 = 35
16 (spell power) * 2 (weakness) * 1.5 (best case scenario) - 25 = 23 * 5 = 115
40 (spell power) * 1 (worst case scenario) - 25 = 15 * 5 = 75
40 (spell power) * 1.5 (best case scenario) - 25 = 35 * 5 = 175
Even if Rydia has at least 12 Wisdom, she would still do a damage range of 60 to 140...
Rydia having approximately 8 Wisdom (pretty much what she has at level 1) would do damage of 40 to 105.
In conclusion, Cute Chocobo > Old Man.