Fade-out: Drawings on the canvas do not last forever (unless you take a screenshot). They fade out after a certain amount of time depending on the room, adding to the fast paced nature of DoodleToo. In the five main rooms, fade-out time is typically around 1 minute.
Ink limit: A limit on how much a user can draw. The amount of ink a user has gradually regenerates over time once exhausted, and registered users get even more ink at their disposal. This is a negligible problem if the user sketches with thin lines. For thick lines, or scribbling, a user's ink can be exhausted pretty quickly. The ink limit is usually the only means of defense against most trolls on DoodleToo, as they tend to rapidly use up all of their ink from scribbling. However, in rooms like Endless (or if someone is using hacks), there is no ink limit.