As he looks now I would instinctively try to kill it.
Point taken. It is indeed a threat, and should be avoided most of the case. There will be some way to disable inkjets permanently, but only in some circumstances, and -- as Mathias will enjoy -- not through Bilou's typical ways of attack. Throwing a dumblador here will only produce a glassy sound, and trying to jump on it will only reveal to the player that inkjets can be used as bumpers.
To some extent, part of the story of Bilou lies in the resistence to those instincts, and use those dangerous denizens to overcome the challenges.
If its a platform, try putting a lid on the bottle (probably a light colour e.g. off-white or yellow).
Let him look happier normally then his eyes squint (rather than being so angry) as he shakes from side to side, then the lid pops off and you can ride the lid up.
good piece of advice, but I prefer keep his current look that match its role in the story, and figure out ways to use something else as a moving platform where I really have to.
If something is attacking, I attack back. And I expect to be able to have an offensive effect - i.e. damage/destroy it.
When I encounter an indestructible enemy in a game, I always resent it.
And that's the established rules for an action game. So I realise that it will be important for me to make sure that alternate behaviour (where the right move is *not* to attack back) leads to secrets or alternative routes, but that I do not force it on the straightforward path so that every player can make it through, just like Mario series do not use advanced technique as the "only one path" to get to the exit.