Courage has no cast time and does not interrupt Garen's previous orders.
Courage's passive bonus resistances are not lost while on cooldown and are calculated after reductions (when the bonus value is lower than the reduction one, Garen is considered as having no bonus resistances at all, therefore not getting any from Courage's passive)
Active:Garen rapidly spins his sword around his body for 3 seconds, losing the ability to basic attack but dealing physical damage (increased by 33.3% against enemy champions and monsters) each second to enemies within range for the duration.
Judgment cannot be interrupted by crowd control effects (Garen does not channel for the duration) but silencingGaren will prevent him from reactivating Judgment early.
Garen will benefit from Decisive Strike's slow removal and bonus movement speed while Judgment is active (he will not be able to silence targets or deal them Decisive Strike's bonus damage since he cannot basic attack for Judgment's duration)
Garen may cast Demacian Justice while Judgment is active (will stop ticking if so)
Judgment's can critically strike but the base damage cannot (only the one from its bonus AD ratio) while also suffering a - 50% critical strike damage penalty (150% AD from 200% AD, increased to 200% AD from 250% AD by purchasing Infinity Edge)
Despite lasting 3 seconds, Judgment's first damage tick is applied right after Garen casts, with 5 more ticks every 0.5 seconds afterwards (the last one does not deal damage)