From Archon Arcana - The KeyForge Wiki
Obsidian Forge • Dis • Artifact • Uncommon • Action: Destroy any number of friendly creatures. You may forge a key at +6 current cost, reduced by 1 for each creature destroyed this way. If you forge a key this way, destroy Obsidian Forge. • Artist: Hans Krill • Card Number: WC:093, MM:025
Artist: Hans Krill
No. If they are not “destroyed this way” they do not reduce the key cost.Source: Rulebook
If I use Obsidian Forge (WC 025)'s action and choose to sacrifice one of my creatures that has a ward on it, will that creature reduce the cost to forge that key?
No. If they are not “destroyed this way” they do not reduce the key cost.