OK it works like this.
Player #1 has Ursang active with 2 energy.
Player #2 has something else, I'll say Sableye PK, also with 2 energy.
Player #1 uses Bad Temper. Sableye takes 0 damage (is resistant), is confused, and has that crazy extra damage effect put on it.
Player #2 now gets to choose if they want to attack or not. If so they have to flip for confusion or take 3 damage counters ... and note that you CAN'T add damage to something that does damage counters.
So if they flip tails, they loose and take 3 damage counters.
If they flip heads the effect will vary depending on which attack is used and who they target.
If they use Down Draw then they just get two cards ... you can't add damage to something that doesn't do damage.
If they use Feint Attack and target a benched pokemon they will only do the normal 20 damage. Bad Temper specifically only adds to attacks against the ACTIVE pokemon.
If they use Feint Attack and target the active pokemon they will do 80 damage (20 base + 60 from Bad Temper).
...
It's also interesting to use Fient Attack as an example because it ignores effects on the defending pokemon .. but Bad Temper is an effect on the attacking pokemon so it does enhance Feint.
If Player #2 could get Sableye unconfused somehow ... like using Double Full Heal ... then Sableye would still get the +60 damage but wouldn't have to flip for heads.
Bad Temper does work on Pokemon immune to confusion (say one with Holon GL and Grass energy) ... but wouldn't work on one immune to all effects of an attack (like a one with Holon WP and Water energy).
The Bad Temper effect would be removed if the affected pokemon got sent to the bench ... so you can't retreat and then switch back up and still get the extra damage.