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megaman_01.cbr
megaman_02.cbr
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megaman_fcbd_2012_special.cbr
megaman_fcbd_2013_special.cbr
megaman_fcbd_2014_special.cbr

During several key issues spanning Archie's Sonic the Hedgehog, Sonic Universe, and Sonic Boom, Megaman crossed over for World's Collide and later World's Unite. Below is the recommended reading order for those story arcs:

Free Comic Book Day 2013
Mega Man #24
Sonic Universe #51
Sonic #248
Mega Man #25
Sonic Universe #52
Sonic #249
Mega Man #26
Sonic Universe #53
Sonic #250
Mega Man #27
Sonic Universe #54
Sonic #251

Sonic Universe #76
Sonic Boom #8
megaman_worlds_unite_battles.cbr
Sonic #273
Mega Man #50
Sonic Universe #77
Sonic Boom #9
sonic_worlds_unite_battles_1.cbr
Sonic #274
Mega Man #51
Sonic Universe #78
Sonic Boom #10
Sonic #275
Mega Man #52