Buff and De-buff

Yeah I've used discs beneath the models before, if they're very distinct colours and each colour has a specific purpose that would make them easy to identify.

But it sounds like you have a load of different de-buffs in mind (just going by your examples, I'm guessing you intend more variety than 3 creatures with special abilities)

If you're going to have busy skirmishes, it would probably be worth making your buffs and debuffs very standardised so one coloured disc (or whatever you use to represent it) always means the same thing. Otherwise, with any busy skirmish, you're going to have to be looking up what the buffs and debuffs mean a lot.

I suppose you could use stackable buffs (so say eg you want one thing to give +2 defence and another to give +4, the +4 can be made out of a pair of stacked +2s) to have more variety with less unique markers.

The first thing I had in mind was a Pokemon-like system where your character card is oriented a certain way to indicate a certain de-buff.

But as I read, it seems there's more de-buffs/buffs you want to put on a particular character.

The most obvious one would be a token on the character sheet, but it also seems like you're not using character sheets.

Another idea could be a slot on the mini (a-la X-Wing) that you could put in a chit indicating a status effect.

Maybe poker chips?

Maybe a thin cylinder next to the character model and use colored donuts (which slot into the cylinder) for status? That way you could stack more statuses on a particular character.

I'm just spitting out ideas.

Maybe have holes in your character base and little colored pins to indicate status...kinda like the people in the cars in the game of Life.