Actually this gives me idea for skeleton/zombie based trap
Stealth mode cannot b stepped on like submarine, but they get 1 tile aura that effects any flesh and blood enemy that steps next to them (including sea infantry)
Zombie aura "you suddenly got ambushed by a zombie hiding under you, and the zombie BIT you, now you will soon b zombified like the rest of them"
Aura requires the tech in zombie rebalance topic, and will zombify enemy after a set number of turns unless exorcised or cured
Skeleton aura "a skeleton grabbed your leg from below you, you pulled too hard, now limper your way out of these cursed lands if u can"
Aura doesn't require anything, unit doesn't get damage but loses -1 speed that lasts 2-3 turns, can b removed by healing
Drawbacks for skeletons/zombies acting as traps
•Enemy player can see unit cannot move on a certain tile so obviously something fishy is hiding there
•Even if the unit do get debuff aura, zombie/skeleton has 0 attack in transform mode so can b easily attacked and killed (since they r visible at melee range)
•zombie/skeleton won't have any action remaining after transforming so they can only FLEE (the irony....

) however this drawback can b removed by giving an action increasing buff spell (if undead have any such spells) or if a special (and weak) zombie rusher like unit is implemented with higher speed and 2 action, then he can counter attack after transforming
Whether this (and other traps) work on giant units is debatable