Looks like it could be interesting to play with. I'm a little confused on your meaning here though.
Contact, as seen in the card, is defined as whenever the target creature attacks or is attacked. However, spells and effects do not go toward this.
Can you give a couple examples to illustrate?
Okay, so let's say the target creature has Gravity Pull. Any creature that that deals damage to the target will, in turn, take one damage.
Also, if the target creature attacks another creature (via Gravity Pull) or the player, they will deal additional damage due to Spines. This does not work with Guard since it replaces the ability,
However, damage induced by spells (e.g. Fire Bolt, Ice Bolt) or effects (e.g. Eagle Eye) to the target creature will not activate the effect.
"I'm well aware of Porcupine | Giant Porcupine."
then you shouldnt have posted this, imo.
That was to pre-empt anyone linking that card idea. Also, after some discussion with Rutarete, I've concluded that this is different enough, but still close enough that some would bring it up.