iserith
Magic Wordsmith
No. And this is ok. Because there is no statblock for Xilonen the polyp. A good use of reskinning.
A bad use would be:
A gigantic gelatineous cube like you encountered several times before. Suddenly arms are coming out entangling you and pull you in.
Not too bad. Could be some kind of mimic. No it is a roper. Surprise. Actually that use would not be too bad because it would actually be a mimic functioning similar to a roper and looking like the gelatineous cube.
To make the thing perfect you add the sticky trait which all mimics have...
Ok I think a roper is a good monster that might be used for many things if you slightly alter its traits so that it fits. My problem is when you actually have stats for a monster and then decide to just ignore then using a different statblock. And it is more than dodgy if somehow any familiar ends up having the owl traits. If the intend had been a pet that flies in and out gibibg advantage all the time the spell would have just told you so. No matter what outlook, the familiar has following abilities...
Actually a hawk with flyby attack that is no familar but a ranger's pet would be more comvincing because a real animal can be trained. A familiar not.
I think what you're describing is actually a symptom of a failure on the DM's part to telegraph the threats the monster poses (so it becomes a "gotcha") combined with the players engaging in what the DMG calls "metagame thinking." It's not reskinning per se that is the issue. There's an underlying problem of presentation by the DM and bad assumptions made by the players that combine to create an undesirable outcome. If the DM telegraphs the monster properly such that the players have reason to suspect that this isn't the thing they think it is, while at the same time the players never take anything at face value and take steps to verify their assumptions before acting, then there is no issue here.