In the ability page...it stated "All new abilities start at level 1. There are ways to improve the level of your ability but we cannot tell you " Anyone has any idea how to level the abilities levels? --And.. sorry if i sound noob..xD
They can be worth it if you're interested in the battledome. They can be helpful in battle... But you have to decide if they're worth it because in order to be EXCELLENT in the battledome, your pet will need good stats as well-- and a somewhat decent if not really good battledome set, which is often a lot of NP. But there are lots of BDers with average stats and BD weapons with wins, so it's really up to you.
My pets don't hav any ability, but with some good weapons I still manage to beat pets twice as strong as mine.
Living proof that good BD equipment is NECESSARY for wins, and can also be more effective than high stats!