As a monster, you really don't need to give it items or feats, just give it a few interesting abilities and adjust it's CR up accordingly. Indeed cherry picking items or feats for a monster may create synergies that make the monster too strong for it's CR.How would you boost an Incorporeal Undead?
What Feats would you choose?
What items would you give it?
(citations fron any 3.5 book/source are welcome...)
Is there anything supporting a summoner can change out a summoned creature's feats? Also the HD increases from leveling up the shadowdancer only specify increasing "(and the requisite base attack and base save bonus increases)" and even if the shadow does get more feats, it only seems logical those feats would follow the chain the greater shadow is on; Mobility then spring attack.[MENTION=1164]frankthedm[/MENTION], [MENTION=6678119]Jackinthegreen[/MENTION] sorry for not specifying the creature...
We are talking about a Shadowdancer's undead companion.
Thanks, though TBH it makes much more sense that the HD do add skills and feats. My concern was adding more oomph to a critter that slings out 1d6 STR damage a round, but that is more personal bias...I can see frankthedm's logic on the matter, but this is something to work out with your DM.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.