What power level?
Are you willing to consider half-undead?
Although the plant monster (after truly dozens of play-throughs of Arcanum, I have to think of it as a Shambling Mound) is what really catches my eye. But a Large Plant costs 17 RP. 18 if you want the reach to make Large pay off. They don't give you enough drawbacks (IMHO) to make it palatable.
So what about skipping Large? In favor of amazingly bizarre?
Plant (10)
Medium (0)
Slow Speed (-1)
Mixed Weakness (-2): +2 Str or Con; -4 Dex; +2 Cha; -2 Int or Wis [note that Intimidation works off Cha]
Standard Languages (0)
Racial Traits
Plagueborn (1) [since you eat carrion]
Stability (1)
Sticky Tongue x2 (4)
Other ideas
Bond to the Land (2): Forest or Swamp
Hydrated Vitality (3) [thematic, but probably over-priced]
Lifebound (2)
Terrain Stride (1): Forest or Swamp
Relentless (1)
Carrion Sense (1) [thematic, but probably useless]
Treespeech (2)
{EtA: Consider bloodrager w/ an Undead bloodline as an option over a multiclassed barbarian.}
Power Level is Standard, Advanced, or Monstrous. At 12 or so RP, you're probably not Monstrous. But getting Advanced traits as options changes things a bit. For instance, you can get a Slam attack, or (if you can come up with 4 RP) Scent.
Sticky Tongue was because of your idea of grabbing things and slowly digesting them. It's not a "tongue" like a frog's, just a vine or something of that ilk that you snap out and grab prey with. It's R.E.A.C.H.
If you go with a full caster rather than a barbarian base (whether multiclassed or as a bloodrager), you could go with just one level of Sticky Tongue and use it for melee touch spells. That frees up 2 RP.
Treespeech could be really useful, esp if your GM is the sort to make sure you can use features from time to time. And it's definitely thematic. Or sure, it could be a constant string of "Some people came by, moving fast. I didn't notice what they looked like." ("Fast" meaning 20 or 30 feet/round.) You'd want to check with your GM -- is it worth taking at all, and would he give you a cost break for it?
Similarly, I'd love to see you get Carrion Sense for free, maybe as a "bonus" RP over 12 or 13. I can't see it coming up that often, but... carrion eaters can smell carrion! You almost have to have it.
{EtA: Note that the stats I had suggested were based on your "all I need is Str & Con." If you go caster, you'll want to reassign them!}
{EtA [2]: If you go full caster, you'll also want to consider Fell Magic (3 RP). It's expensive, but +1 to DCs for a school saves you a feat (or doubles the benefit if you take it anyway). What I'd love to do in your shoes, going full caster, would be to find out what your GM would charge you for a special Racial Trait (which you'd probably want to rename, incidentally) --
Death-Aligned Magic (2 RP?): Prerequisites: None; Benefit: Members of this race gain +1 to the DC of any saving throws against necromancy spells that they cast. They also gain a +1 bonus on caster level checks made to overcome spell resistance against necromancy spells that they cast.}
Sorry, I've been away. What's happened?
If you went caster, I hope you were able to get Death-aligned Magic.
As an alternative to necromancer, if it's not too late, what about the Empyreal Wildblooded Bloodline, based on Celestial? It uses Wisdom, and the Sacred Cistern power replaces the terribly non-thematic flight.
Although Verdant looks good too.
So sad. Good luck on fleshing out a fun concept someday!