It's cute but Tarmo has not been good enough in some time. I do not think this adds enough to the mix to make it worthwhile, since in order to activate his card filtering you likely need to have Delirium turned on already in the first place. For the mana your paying in the colors you are in I think I would sooner be casing Abrupt decay, but I also think the deck that is playing that does not want a wealth of small creatures (Oath likely.)
The effects seems adequately strong, but I wonder if it will be too difficult to have him connect? Between Eldrazi, Mentors, Pyromancers and the Human mirror, connecting without him dying seems hard.
In a classic Human build it might even be difficult to reach Delirium, but filtering on its own would be ok. And it would help manage damage from Dark Confidant.
If only he had some kind of evasion - I don't think he will be succesful in this meta, but I hope I'll be proven wrong
this seems like another card that is on the verge of playability, this may see play but im not sure, as uvatha has said, with all the creatures running around it might not be good at the moment. if mentor, eldrazi, and young pyro werent everywhere i would say its great. as someone else said in another (diferent card but it applies here) good card but in the wrong meta.