mammoth is so easy to kill it isnt funny
heres a guide to killing it for each nod vehicle

buggy:runn up to and wait to blow up plant c4 and blow them then run
apc:same as above but with more techs
light tank:get sideways and go back and forth while shooting at the mammoth
example the | is the light tank its it going up and down the M is the mammoth its not meving because only an idiot tries to dodge in a mammoth

^ going up and down
|- <turret> M

flame tank:get right up agaisnt it and it cant hit you for more than a 20 amor/health per shot then flame away

stealth tank:lay in wait and when the mammoth passes shoot shoot shoot until it dies even if the guy has the camera follow turret option enabled hes a dead man

there we go the complete guid to killing the joke that is the mammoth tank