Does Heimerdinger trigger all exhaust abilities of your cards simultaneously when exhausted, or does he gain those abilities and you choose which one to activate?

Ruling: Heimerdinger does not trigger all exhaust abilities at once. He gains all exhaust abilities from your cards, and you must choose which one to activate when you exhaust him.

Nuances:

• Heimerdinger copies the abilities themselves, not their effects
• You still need to pay any additional costs (like energy or power) required by the chosen ability
• Only one ability can be activated per exhaustion