To spike a foe usually means using an important quantity of resources for a single fight (usually a boss).
To its larger extent, these resources could be anything :
- Monster Xp (for level-up's, see popcorn)
- Exploration (for longer the average regen-fighting)
- Conversion points (when it provides a temporary effect)
- Death protections
- Blood pools
- Gold (when it provides a temporary effect, such as the crystal ball)
- well anything else you can make use of, and that is in limited quantity...
The devs have given the most concise explanation of spike with: "Draw a graph of damage output, if it spikes, that's a spike.", even though it was the players who came up with the term when trying to map out the different approaches to playing the game.
An idea behind "spiking" is that a run cycles through 2 phases:
- The setup, during which the player explores the dungeon and hoards/saves various resources
- The execution, during which the player spikes tough opponents, boss or bosses, consuming an important part of these resources.