I've tried this unsuccessfully a few times, and here's some things you need to be aware of:
1 - Level 10 mobs may hit weak, and may do very little damage, but it adds up fast when there's 20 of them. Your best bet for a train maker is a pld.
2 - After you use astral, all the mobs will hate your avatar, and the one that you targeted will have a tiny bit of hate for you. Your avatar will die in a split second, and the one you targeted will come for you. Easy way to fix this is to target a weak one that you know will die.
I would suggest for mob choice:
1-3: Mouse Bat, King Ranp's Tomb
1-3: Watch Lizard, Ghelsba Outpost
3-5: Goblin Thug/Goblin Weaver, Dangruf Wadi
5-8: Grotto Bats, Yughott Grotto
8-11: Wadi Leech/Wadi Hare, Dangruf Wadi
10-12: Goblin Ambusher/Butcher/Tinkerer, King Ranp's Tomb
12-15: Stink Bats, Ordelle's Cave