I know this issue was seen before with other users but how was this fixed? By pet is happy and fed because he's in the resort but when I go to battle it says none of my pets are eligible.

Have you checked your stats page to see if he's stuck in a battle?

[edit] Actually, it looks like he's got no hp. ^^

Hah I guess it's been that long since I last battled with him I forgot to take him to get healed. Well don't I feel silly x.x Thank you!