Part 2 of my 8th edition Imperial Knights codex review will take a look at the Stratagems available in the new book.
Ion Aegis (2CP)- Use at the start of your opponent's movement phase. Choose a Dominus Knight in your army. The Knight cannot move until the end of the next turn, but all friendly Imperium units wholly within 6" of the Knight gain a 5+ invulnerable save against ranged weapons.
This is a pretty strong stratagem if you don't get the first turn. This will work really well for some Imperial allies you may wish to take with your Knights, with the Guard Battalion for command point farming. This will be strong for the Knight Castellan, which has a lot of powerful, long ranged firepower. As this works on the whole unit, you may not get a lot of units in range, but it still should still help a number of units.
Noble Sacrifice (2CP)- Use before you roll to see if an Imperial Knight explodes. On a 4+, it explodes. If a Dominus Class Knight, roll two dice, if any is a 4+, it explodes. If both dice are 4+, then all units in 3D6" are affected.
This could be quite powerful in the right cirumstances. Doing D6 mortal wounds to nearby enemy units after losing a Knight could help to kill their attackers (if in combat) or damage nearby enemy units. I don't see it being used too often, but could be key in a few games.
Thunderstomp (1CP)- An enemy Infantry unit (or swarm) within 1" suffers D3 mortal wounds on a 4+. Titanic units only.
A cheap way to do mortal wounds to an enemy unit in combat to finish them off. Though, Knights are tough to tie up in combat now, so may not be necessary much of the time.