Finishing blow may come from any prescribed elemental source in the party, including avatars.
Meriphataud Mountains (S) — Treant Sapling — (K-5), This camp is very easy to access, low risk, has 8 Saplings on 5 min retimers and the mobs are just high enough lvl to all give ~10 exp to lvl 95. Right: Screenshot of spawns.
For a 99RDM/45SCH, Two-shotting would be highly difficult barring another MAB staff (Vourukasha I), outstanding gear, or outside support (Avatar's Favor, Wizard's Roll, etc). At 150 INT and +40 MAB, Ionohelix and melee make an effective combo, with Thunder IV hitting for around 50-55% of the sapling's health.
Caedarva Mire->Mature Treant/Treant Sapling, near the pond at (I-7). If you're careful, you can make a small train (6-8) of Saplings without aggroing/linking the treants and then proceed to kill them with -ga spells. Be careful and don't fight close to the pond (Jnun will detect by sound and HP during the night, and the slimes detect by sound), and not close to the treants either (aggro by sound). You can also kill the treants if you like, but they're tougher and have a lot more HP.