fleet hemlock
I like this card but maybe it'd be useful to know mid-range to keep a distance by making visuals or auditory cues (or both).
This is a trap card so I don't think it should be abundantly clear that this card was used but if someone's paying attention, they'll know what's up.
pastel sedge
Something like making the enemy beep periodically when it's active and having their stomach flash red every time the beep happens (since the card art implies that you're swallowing a bomb) would not only help attentive players avoid getting kamikazi'd, but it would also be a nice audio/visual detail.
gleaming river
Trap cards are meant to be secret moves that only activate on "certain condition". Knowing for sure that someone activated self destruct would make you less careful with cards usage since you know it's not mimic or counter for example