Scarecrows/
shapeshifter with Changeling and champion a creature.
Champion an [creature] (When this enters the battlefield, sacrifice it unless you
exile another [creature] you control. When this leaves the battlefield, that card returns to the battlefield.)
Example 1:
Changeling Berserker {3}{R}
Creature —
Shapeshifter5/3
Changeling (This card is every creature type at all times.)
Haste
Champion a creature (When this enters the battlefield, sacrifice it unless you
exile another creature you control. When this leaves the battlefield, that card returns to the battlefield.)
2-3 champion a creatures can cause an infinite loop of ETB., the commander makes them free/cheap
Reaper King just drops down for FREE!. shapeshifters with changeling is ALSO scarecrows (The betters scarecrows XD) also
reaper king just pops every all opponent's board including all opponent's lands if you want. proceed to win from here.
abuse that infinite etb for the win.