The ninjutsu ability can be activated during the declare blockers step, combat damage step, or end of combat step
Using my Ayli deck as an example, the idea of switching the general to Tymna the Weaver, or Teysa, Orzhov Scion, is probably counter-productiveboth of these Commanders synergize much better with a token strategy/swarms of creatures, and might make my deck, aiming to be a 6, actually stronger
While this list could be exhaustive, and include spells such as Lightning Storm and Tormenting Voice, remember that my main intent is to quickly show the major incentives to play a color and some general powerful cards to watch out for
Zhulodok, Void Gorger, Omarthis, Ghostfire Initiate, Endbringer, Kozilek, the Great Distortion, Ugin, the Ineffable, Rise of the Eldrazi, Endless Atlas, Investigator's Journal, Mazemind Tome, Mystic Forge, Ugin's Mastery, bleh to Hedron Archive and Dreamstone Hedron 13 card draw