An example of a surprising result is if you have a pokemon with the ability volt absorb and a stunfisk that knows thunderbolt then you can use thunderbolt on your ally which will heal it and have your ally use discharge and your pokemon are completely healthy while your opponent will be heavily damaged.

You can also have stunfisk us scald on a vapereon or lapras and then use a powerful attack with the same results.

If you have a darkrai, have it use dark void in battle with a pokemon with the abilties: insomnia or vital spirit.

Also the abilities Rain dish and drizzle, and drought and chlorophyll work great together.