The Infiltrator has a few subtle disadvantages to his snake cousin: 1) You need to play two colors to play the Infiltrator, instead of one for Ophidian
After three years and 13 sets, some early cards would be so powerful or so ubiquitous that new sets couldn't compete
You lose out on a few dorks like Copper Myr and Leaden Myr but compensate for it by keeping access to Sarcomite Myr and Parcel Myr
Kaervek the Merciless Cast a spell, take a bunch of damage! Now sing that to the tune of that one random Lion King song: Dig a tunnel, dig-dig a tunnel! Youd better hope your life totals high enough when Kaervek the Merciless hits the board, otherwise you might find yourself locked out of casting spells
Any one of these mentioned below would be really good inclusions in your decks
When it's defeated, exile it, then cast it transformed.) When this Siege enters, return up to three target permanent cards from your graveyard to your hand