a simple bonus trick has come to my mind:
how about implenting a "Secret Bonus" that will be randomly selected when the Match begins.
the Secret Bonus will be implented on one random Tile
and when you "eat" your enemy on that exact Tile , you will get a bonus.
now what im thinking of is somekind of a "Soldier" changer.
so for example you have the simple Pawn and that Pawn "Ate" an Enemy Soldier (of anykind ) you will see a little Suprize
and a message of " Please Choose your Soldier" then you can change that Pawn into a Queen or a Turret , or a Horse or whatever you want
i think its a simple idea and can be implented with Ease.
also , you can do a Crazy Bonus which work the same way as the Secret Bonus only that this one will randomly change your Soldier into what ever the computer randomly selected.
so if you have a Queen and you Ate and got the Bonus , suddenly you see an Evil smiley lauging at you as the Queen changed into a simple Pawn
but if you have a Pawn and got the Crazy Bonus you see an Awesome Smiley or something that changed it into something better .
and thats also simple to implent the smiley idea
Queen is 6
Runner is 5
Turret is 4
Horse is 3
Pawn is 1
so if Queen or Selected Soldier is BIGGER ( > ) then Randomly selected Crazy Bonus you get an Evil Smiley as it was better then the new Soldier ,
but if Selected Soldier is SMALLER ( < ) then Randomly Selected Crazy Bonus , then you get the Awesome Smiley as that now you have a better Soldier then before
simple ha?
once this is done , you put like 3 to 5 , and maybe an option before the match begins
" How Many Secret / Crazy Bonuses on Plane ??3 - 4 - 5 - 6 - 10 etc"
if you liked it , Glad i can Help
Edit : Sorry for the Horrible English it is my second Languge.