Talk about a stubborn weed that simply won’t stop growing! In many cases, Phytotitan will come back and be relatively useless for a turn. This is because upkeep comes after the untap step in a turn. That is, unless you find a way to untap it and give it Haste, of course. But being able to have a 7/2 creature that can survive board-wipes and perform on both offense and defense is extremely strong in Limited. Also, in Magic 2015 draft and sealed deck, Life’s Legacy and Phytotitan were quite valuable together. Life’s Legacy sacrificed Phytotitan and drew you 7 cards.
Understandably, Phytotitan never saw Standard play outside of some rogue decks. Being a 6-drop that is essentially useless for a turn when it returns is most likely going to be too slow for any competitive format. Some rogue Commander decks found a use for it, however. Jarad, Golgari Lich Lord decks occasionally saw use for its 7-power. His ability allows you to sacrifice Phytotitan to deal damage equal to its power to each opponent. It never became a staple in that deck, however. In some rare cases, Kresh, the Bloodbraided, Shattergang Brothers, and Xenagos, God of Revels decks used Phytotitan as a budget option.
Another cool interaction with Phytotitan is with the once very popular The Mimeoplasm. His clone ability would allow you to copy one creature while inheriting the power of another creature in the form of +1/+1 counters. Because of Phytotitan's ability to return to the battlefield, the Mimeoplasm would actually come back, although not as a Phytotitan. The Mimeoplasm would then need to choose two new creatures in order to not just hit the board as a 0/0 Ooze and die, but it's a nice little interaction that worked in some Mimeoplasm decks.
But, it wasn’t until the release of Omnath, Locus of Rage in Battle of Zendikar that Phytotitan found a real home. Being an Elemental, he fits perfectly into the Tribal theme of the deck. Bringing him back tapped is perfectly fine. His main purpose in the deck is to activate Enchantments like Elemental Bond (draws you a card) and Warstorm Surge (deals 7 damage to a target creature or player). Life’s Legacy, the card that it worked with so well in Magic 2015 Limited, is sometimes played in these Omnath decks, too.
Phytotitan is an example of how many of Magic 2015’s rares destined to be bulk are still flavorful enough to become good cards in casual formats and in Commander.