I'd propose that fighting a tactical battle on a shard tile be a special experience. There are several things I'd like to see, but I'll put the most important first:

1. As the repositories of all magic on Elemental, the shards should have significant magical effects on battles being fought in their squares. These effects should be amplified for the owner of a shard when a structure has been constructed to channel its power.

• Death shards: Universal effect: All undead creatures gain one hit point every turn. All living creatures lose one hit point. No life magic spells may be cast. Owner effect: Death magic spells have their damage or effect doubled.
• Life shards: Universal effect: All living creatures gain one hit point every turn. All undead creatures lose one hit point. No death magic spells may be cast. Owner effect: Life magic spells cast by the shard owner have their effect doubled.
• Water shards: Universal effect: Ice elementals gain one hit point every turn. Fire elementals lose one hit point each turn. Owner effect: The shard casts chaos on a random enemy unit; the shard has a minimal initiative so this doesn't happen too frequently.
• Fire shards: Universal effect: All fire elementals gain one hit point every turn; ice elementals lose one hit point each turn. Owner effect: All fire spells take effect as if the owner controls one more fire shard than they actually do.
• Earth shards: Universal effect: Fire, water, and air spell cannot be cast in tactical combat on an earth shard square, with the exception of dual-school spells that include earth (Natures's call, Sunder, Stinking mud). Owner effect: a level 5 (+1 level for each earth shard owner controls) earth elemental is summoned and put under the control of the owner's army by the shard once at the beginning of combat. The summoning of this elemental does not cost the owner any mana.
• Air shards: Universal effect: Air spells cost no mana. Owner effect: Owners army starts combat with Guardian Wind and battle cry cast on them.

2. The shard should be visible on the tactical battlefied.

3. Tactical terrain appearance and behavior should be affected by the presence of the shard, so a fire shard should have pools of lava that cause damage to any unit susceptible to fire passing through them, earth shards should have impassable rocks, water shards should have swampy areas that double movement cost, air shards should have foggy areas that increase dodge for units standing within them.

4. This had already been suggested previously in another thread, but I'll repeat here the suggestion that shards initially be guarded by variable neutral creatures of types that make sense for the node type.