Just putting this up as a repository of information on Ryu’s Denjin mode. Please add tech, setups, videos, and questions on Denjin mode here!
 Denjin Mode is activated by using the V-Trigger command (HP+HK). V-Trigger can be cancelled into from any normal, or from the final hit of Ryu’s target combo. You can’t V-Trigger off any specials or command normals.
 Denjin Mode lasts a predetermined amount of time (around 12 seconds), although this timer is reduced by a chunk with each Hadouken you throw.
 Hadoukens are improved in Denjin Mode. They travel considerably faster, they deal 70 damage instead of 60 and 150 stun instead of 100.
 You can also charge Hadoukens. When fully charged, Hadoukens will deal 120 damage, 300 stun, and break guard, giving you +32 advantage to go in and punish fully. This will not allow a jump-in, but it will allow a dash-forward followed by a Solar Plexus Strike.
 All Hadoukens will now knock down as well.
 Your damage after a Hadouken guard break is scaled to about 60%
 EX Hadoukens charge fully much more quickly than normal Hadoukens, and will deal 150 damage and 300 stun.
 Critical Art also breaks guard in Denjin Mode, leaving you at +8, enough to link a cr.HK. Critical Art also deals 350 damage instead of 320 and 300 stun instead of 0 stun.
 All moves that use Ryu’s fists are buffed in Denjin Mode.
 Ryu’s punch normals all deal 30 more stun. So st.LP deals 100 stun instead of 70, and st.MP deals 130 stun instead of 100.
[*] Ryu’s Shoryukens all deal 20 more damage, and 50 more stun.
Denjin Mode seems especially useful in these scenarios
 Using the V-Trigger as a combo-extender. This can usually lead to 100-200 extra damage in a combo, depending on positioning.
 Using the V-Trigger to improve reactions for better punishes. Once you have full Critical Gauge, you can threaten a V-Trigger into super to punish a great deal of moves that would ordinarily be quite difficult to react to with the super input normally.
 Using V-Trigger to make moves safe. Cancelling cr.HK into V-Trigger on block is sometimes a good idea, especially if your opponent can threaten a big punish to your sweep.
 Using Denjin Mode to set up an unblockable Hadouken. This is tricky, as ultimately even the EX Hadouken is incredibly slow to charge fully, and is the equivalent of catching someone with a relatively slow overhead. It has the added advantage of being able to release early, the idea being that the only defence against a fully charged Hadouken is to jump out of it, but releasing it early will catch them on their way up. This is ultimately a guess situation, and the risk reward isn’t great for you, as you’ll only really get about 170 damage off a guard break without super.
[*] Using Denjin Mode to threaten stun. I actually think this might end up being one of the better applications for Denjin Mode. The stun damage increase is significant, and applies to many of Ryu’s best pressure moves, such as st.LP, st.MP, and cr.MP. Given Ryu already has a very good stun potential, V-Triggering to complete a beefy combo will likely put your opponent in a situation where one more combo will stun them, likely ending the round.