anything would be better than everything
Anything: "Mon chien mangeait n'importe quoi, même les moustiques."
In English you wouldn't use "everything" in the future. You could say "my dog eats everything"
There is no future tense in this sentence. Mangerait is present tense, conditional mood. The future tense is mangera.
Besides, we use "everything" in the future tense all the time, if that were actually an issue here.
How do we know même means "even" here and not "like/ the same as"?
Good question! I thought at first it meant "My dog would eat anything, and so would mosquitoes."
C'est dégoûtant, ton chien.
Where can I find a dog like this?