Okay, this is really just a wording issue, the spell’s actual effect is fine, but Caribou’s spelltext (as of its release today) says:
… Really, zero to three? There has literally never been a summoner who is allowed to successfully summon zero troops – the preferred wording is instead “There’s a [__]% chance to summon…”
Suggested wording for Caribou:
Where the stated % is the calculated probability of summoning a nonzero number of troops. (For example, assuming each value from 0-3 is equally weighted, this would be a 75% chance to summon)