Onfim

First Battle:
1) Meditate
2) Haste (targeting Levi )
3) Rally (targeting Levi )
3) Defend
4) Eliminate

Meditate, haste, and rally will generate enough breath to cast eliminate. You need to defend because you still have 1 turn left before the penalty of meditate wears off.

Second Battle:
1) Haste (targeting Levi )
2) Rally (targeting Levi )
3) Eliminate

Using haste will give you a free turn (it uses a turn and adds a turn), as well as allows your dragon to keep up with the monsters. Rally increases your attack, and eliminate all the enemies.

Enemy Attack Order:
Hit the melee enemies first, and the mages last. The mage has a chance at charging instead of attacking so you won't take more damage.

Sap Usage:
I tend to use sap when there's one mage left, and it attacked because it has to meditate.

You can also use 3 saps on the last mage if you have the breath for it, this should gain you more health than you lose even if they attack.

The more you play with the Levi build, the more comfortable you'll be using sap. I've had a few times where I got my fodder from 1 to 7 without stopping because of sap, but that's uncommon. It's more common that using sap will let you stay for 1-3 more battles.

Refresh:
When training fodder and need to refresh, I suggest putting the fodder's stats into vitality so that they can take more hits instead of your trainer. In contrast to the Mire, this helps a lot in the Kelp Beds, and it is worth the small amount of time it takes.

This isn't really needed if you're training to level 5, but you can still do it if you want. It's most helpful if you're training to 6-7 or higher.

Dodge:
If you miss an Elim and don't have enough breath to cast it again, you should refresh. The only time you might not need to refresh is when there's only 1 caster remaining: then you can decide if it's worth setting up your breath again.

Note: If you're 5-10 breath away from Elim, you can cast Haste + Rally to get that breath instead of casting Meditate.