{But when} (epan de). Note hotan in verse  21 .
{Stronger than he} (ischuroteros autou). Comparative of
ischuros followed by the ablative. {Come upon him and overcome
him} (epelth(936e) nik(8873)(8869) auton). Second aorist active participle
of eperchomai and first aorist active subjunctive of 
ika(935c).
Aorist tense here because a single onset while in verse  22  the
guarding (phulass(8869), present active subjunctive) is continuous.
{His whole armour} (	(886e) panoplian autou). An old and common
word for all the soldier's outfit (shield, sword, lance, helmet,
greaves, breastplate). Tyndale renders it "his harness." In the
N.T. only here and  Eph 6:11,13  where the items are given.
{Wherein he trusted} (eph' h(8869) epepoithei). Second past perfect
active of peith(935c), to persuade. The second perfect pepoitha is
intransitive, to trust. Old and common verb. He trusted his
weapons which had been so efficacious. {His spoils} (	a skula
autou). It is not clear to what this figure refers. Strong as
Satan is Jesus is stronger and wins victories over him as he was
doing then. In  Col 2:15  Christ is pictured as triumphing openly
over the powers of evil by the Cross.