I think there are 2 possibilities:
a) We use the existing rules and make Tsunami work like those
b) We want Tsunami to do what you would expect from a real Tsunami
In Mage Wars, b) is equally important to a) I would say.
As Zuberi summarized you can already use a).
As Kelanen summarized, you could make b) work as well. It only needs 1 additional sentence on the card:
"After its initial zone attack, Tsunami becomes the source of subsequent zone attacks."
Note that this will mean, that any wall Tsunami will cross will stop it from moving further, because there would be no LoS from Tsunamis current zone to its next zone.
Although I was heavily in favor of making Tsunami work more real, I'm now more and more for variant a).
Because:
- It uses existing rules.
- You can easily almost make it work like a real Tsunami would, by cleverly casting and pushing.
- It gives you more strategic possibilities to use the spell, like making sure it does not stop at a wall that blocks LoS.
- It doesn't create other problems with spells that address the "caster of the spell".
Having a Tsunami travel one direction, but resolve pushes perpendicular to it (or even reversed from it in the first zone) is weird and non-intuitive. It's well-supported in rules, but I think this card should be ruled differently.
It is only weird if you consider the Tsunami to be the source of subsequent zone attacks.
It would not be weird if you would describe the card:
"When Tsunami is cast, the mage chooses a direction. After Tsunami is done attacking the zone it was cast to, the mage may cast Tsunami again to the next zone at no additional mana cost, following the chosen direction while ignoring the spell distance. Tsunami stops repeating when it reaches an Arena wall. When a situation arises that would not allow the mage to re-cast Tsunami - for example when he has no longer LoS to the zone where the next attack would need to take place - the Tsunami attack stops repeating as well."