The mammoth already has a platform saddle in ark mobile but you have to buy the engram with real money. Click the up arrow if you want to help convince wildcard to add it into all versions of ark fully including ark mobile for free!!! Help start the petition revolution!!!!
They aren't extremely fast and are easily outrun, so just shoot it with a crossbow using tranq arrows and turn around and runa. Few steps when it gets too close. ( may be best to take out any other mammoths before attempting to tame )
On the raft build a 3x3 foundation with 3 walls high and a ramp going up into the raft. Go to the winter area youll find Mammoths there. Get it into the raft. Once in the raft shoot it with tranq arrows. Starve it and then feed. Kibble is 80times its food.
I tamed a level 40 mammoth, no cheats/tame boost on settings. It ate 100 mejoberry (it said 250 on here) but I needed 102 because spoil times a bummer. It also took 7 narcotics not 76 like it said here. Unfortunately didn't pay attention to how many tranq arrows it took. Hope this helps :)