I can see a couple solutions
1. Obviously, I'd support the attack missions not costing mana because it'd make my life easier... but it also means there's never a reason to not attack. Mana doesn't mean as much in that case, either, so maybe that's more a last resort.
2. Perhaps, when you do issue a movement command, you can also explicitly order the survivor to idle there if he would otherwise automatically do something. If he can automatically do something, the game pops up a menu telling what, and in which order, and you can give an order to cancel those automatic actions in some way or another from there. It should auto-default to select whichever option is most likely for players to select. How often do players move next to impasses without wanting to destroy them?
3. Or, just stick with the above thing and don't include the ability to give an explicit 'remain idle' order. That way, the game pops up confirmation with you defaulted on 'OK' that explains what will happen on that space.
4. Or, the last alternative to plan number 2... have some kind of strategic configuration screen where you can set up behavior. So, you have 3 options for every thing that can happen. Either "Always do it", "Never do it", or "Always ask me." This is probably the most elaborate solution, or an even more last resort.
In summary, either make them more explicit or remove the cost.
Oh, and Zespri, just move adjacent to impasses. That's enough for the survivor to know to blow it up.
