When troops are arranged in rows of three or more, as opposed to columns, they'll meld into a wall, shuffling up to the frontline screen divider. Each faction's wall has a different ability, with the Sylvan's hedges recuperating a hit-point each turn and others being tougher or a little bit shiny. These walls will absorb damage and protect your troops from attack, but take up a space in the grid where you could be stacking troops.
Activate two or more units of the same colour to attack in the same turn, so that their timers countdown together, and their attacks will be linked, improving their attack power. Units can also be "fused" by stacking active columns, coagulating them into one and further increasing their offensive value.
So, battles are largely puzzle-based, but troop and equipment choices are still an important part of a good strategy. Deer, for example, can leap over a single row of enemy walls, bypassing their protection, whilst dragons will leave a two-square swathe of acid in their attack's path, damaging any troops occupying those spaces for the next few turns. The various pieces of equipment which you'll accrue offer fairly typical bonuses, improving specific troop types or upping your survivability.
There are occasional variations on the straight battle theme, too. There are puzzle levels, where all enemies must be defeated from a set position in a single turn, not unlike the Puzzle Quest equivalent. Bosses crop up as well, moving around the grid and forcing you to strike them directly rather than go for a shot to the end zone.
It sounds more complex and less intuitive than it actually is. In practice I found that the hardwired 'put things in lines' part of my gaming brain quickly engaged, giving the turn-based system a smooth ebb and flow - strategies can be planned with surprising depth and foresight, and enemy tactics must be countered before they are unleashed. In many ways it's actually more complex and satisfying than the traditional M&M model. A balance between attack and defence is key to victory, and protecting and using elite or champion units properly can turn a lost battle hugely in your favour.
Altogether it's quite the bold move for the series, even if a lot of the ideas have been quite heavily 'inspired', but looks like it'll translate the core values extremely well. At the end of my short campaign section I was definitely hungry for more - and there are another four factions, each with their own campaign, still to see. How much cross-pollination will occur from the main canon is uncertain, but there's really no wisdom in hating Clash of Heroes because it dares to ring the changes.
Might & Magic: Clash of Heroes is due out for DS in August.