if u have character of elephant, than u get the strongest soldier in the team..make elephant warrior, equip with hell breaker and make 8 all of them. it's expensive though (60 mp) but very strong. i didn't even buff to them..if u don't get elephant yet..try my hint below and defeat them in orce king secondary quest and weapon in devil king
with troll as cavalry using mighty lance, make 8 all of them, then u'll get powerful soldier ever..i used this almost all level in hard and never lose..support them with haste, rage and mini..trust me, It's works!
a little tips from me..
set ur skill to expand mag, bio absorb, bullet shield, bullet explode
then set ur weapon to minigun and gauss rifle..
with this set up..u'll unbelieveble undefeated, i'll try in every level at overgrind, they're just so smooth and i can kill all enemy at every level..
final bos just piece a cake..
at first it soo boring when i jump to slow n upgrade too expensive..
when i get them all, it's soo quick that i feel the door is not enough..
well, i complete this game just for 1,5 hour