But balista could at least attack the wall you place in front of it, the hammer cannot.
Don't you have to have LoS and proper range to a zone that the wall borders? If you put an LoS-blocking wall bordering the zone containing the Ballista, it wouldn't be able to target the wall because LoS to the target zone at proper range (1 zone away) would be blocked. The only zone that the wall borders that is in LoS is at range 0.
From the rules pg 18
Attacking Walls
A creature in either of the zones bordering a wall may make
a melee attack against that wall. Ranged attacks may target
a wall if either of the adjacent zones is in range, the wall is
in LoS. Walls do not occupy a zone, and are not affected by
Zone Attacks or spells that target a zone.
A ballista can attack the wall because the adjacent zone is in range and it has LoS to the wall.
Akiro's Hammer has the "corporeal conjurations" and the 2-3 range to deal with. A fog bank / wall of fire is untouchable by the Hammer
Furthermore since the hammer's zone attack targets a zone any LoS blocking wall can prevent that attack.
Ballista = Awesome
I interpret that text the opposite way (assuming there should be "and" where the comma is). The wall is in LoS but the adjacent zone (at range 1) is not, so I can't attack the wall. The other zone adjacent to the wall (e.g. the zone containing the Ballista) is in LoS but not at a legal range for the attack. At least, that's how we've been dealing with these types of effects.
For example (that has come up), [mwcard=DNC13]Skeletal Archer[/mwcard] wants to attack a LoS-blocking wall that borders its zone. It has to use a 2-dice melee attack because it can't see a zone that the wall borders that is at legal range for its 4-dice ranged attack.
Please correct me if I'm wrong.
Also, the text you quoted has a grammatical error. (Is that a direct quote from the current rules?)
*edit* I was posting this while other answers were coming in. Well whaddya know?! We've been doin' it wrong! Suddenly ranged attacks with min-range of 1 look SO much better.
OK, fine, Ballista doesn't need the Indirect trait, but Akiro's Hammer could certainly use it.
*edit again* And Akiro's Hammer isn't as bad as I thought it was, because the only
corporeal LoS-blocking walls it can't attack are the ones that border its zone (and ones that are beyond 3 zones away, but it doesn't care about those ones). I thought you could put a wall on the border between 1 and 2 zones from AH and block LoS to your conjuration with impunity, but apparently it can target that one despite not having LoS to a zone that's in range. That's very unintuitive based on rules for range (e.g. when casting walls) and even tricky to deduce from the rule book (but clearer in the FAQ). Now, as V10 pointed out, incorporeal walls are the silver bullet against Akiro's Hammer.
I guess that's the only instance where a non-flying non-reach creature can choose between either a melee attack or a ranged attack with minimum range of 1 against the same target.
(I know you can always target a flying creature in your zone with a ranged attack, even if it's inside the minimum range of the ranged attack - but then you wouldn't be able to target it with melee unless you were also flying)
