I Believe that it is currently possible to cast equipment onto an enemy mage. I looked and couldnt find anything to the contrary, but i admittedly just had 4 teeth pulled and the pain relievers the doc has me on are making it tough to recall anything specific. So if the following is impossible feel free to have a cheap laugh at my goofy, borderline stupid strategy ideas. if they do work they are situational at best. This all started with me looking to find a use for Bearskin.
Ok so assuming that one is running rust (cuz its awesome) because it doesnt actually require the target to have armor to stick, like corrode tokens do. Also assuming the opponent already has a chest piece you dont like due to a -2 effect or something similar (harshforge much). One can cast a bearskin over the armor the opponent has (Dragonscale, stormdrake, harshforge ideally with a rune on it! {Though i dont know if the rune gets destroyed or not, it should but im not certain since you can only place each once a game}) and then reveal rust to negate the 2 armor. yes its an expensive 9 mana with the rust reveal, but it nets you their loss of the element -2/-3 and its only about 1 to 3 mana more expensive than the armor itself and you could make them lose a possible rune, damage barrier, or harshforge bonus!
If they want the old armor back they need to either recast it (returning it to your own spellbook to just re apply the next turn for 6 mana [that gets around nullify as well]) wasting a quick action. Or they have to dissolve it so you dont get it back when they re equip the desired piece.
The Same trick can be applied for even less mana with the novice leather gloves and boots. Got a beastmaster or druid up against the walls but they have eagleclaw boots? cast leather boots on them for 2 mana and swap those eagleclaws away for a turn. the rust will negate the armor gain and you've only spent 2 mana (plus the rust i know but its assumed to be there for all these combos.) it works for reflex boots and bracers too. Keep a leather belt and throw that on your opponent once they put on the regrowth belt, make them recast.
I dont know, heh whaddya think? should i wait longer before posting after my next trip to the dentist or does this at least make sense? Its been making me chuckle all day.