How many mono-red damage doubling effects are there?
10 that apply to your commander. (11 if you're willing to do hijinx with Goldnight Castigator.)

Magic: the Gathering has highly standardised ways to word its effects, so when you see an effect you like and want to find more of it, you should search for the words you find in the effect that look like they're fairly unique to that effect. (Recognising which words those are can take some experience.)

You can search in either Gatherer (the official search engine), or a third party search engine like Scryfall or MagicCards.info. I find these second two are far easier to compose searches in. I'm going to be referencing Scryfall below since it's my personal favorite.

If you search only for o:"double that damage" (within a color identity of red, and within the Commander format) you'll find 17 damage doubling effects.

The following don't actually work for your commander:


Charging Tuskodon and Goblin Charbelcher only double their own damage.
Fire Servant won't interact with Kumano.
Blind Fury, Impulsive Maneuvers, and Inquisitor&#39;s Flail only interact with combat damage (which won't count Kumano's ability).


Goldnight Castigator doubles damage to you, but works if you you give it away with Harmless Offering or a similar spell.

We can eliminate the ones that definitely don't work from the search results by name for our perusal.



You may also be interested in damage increasers, of which Tok-Tok, Volcano Born and Embermaw Hellion apply. (You can &amp; should apply these before any damage doublers.)