  The usual range of new particle masses, up to a few TeV, searched for at the
LHC may be substantially extended if ultraheavy diquark particles exist. A
diquark scalar, $S_{uu}$, that interacts perturbatively with two up quarks may
be as heavy as 10 TeV and would still produce tens of spectacular events at the
14 TeV LHC. It is shown here that an ultraheavy $S_{uu}$ could be discovered
through final states of very high energy in various channels, especially if the
diquark can decay into other new heavy particles. Examples include cascade
decays of $S_{uu}$ via a second scalar produced in pairs, which leads to two
dijet resonances, or to more exotic signals with top quarks, Higgs bosons,
electroweak bosons, and high-$p_T$ jets. Another possibility is that the
diquark decays into a vectorlike quark of multi-TeV mass and a top or up quark.
Signal events include one or two highly boosted top quarks and a Higgs boson or
a $Z$, without counterparts containing top antiquarks. Similarly, direct decays
of the diquark into $tj$ or $tt$ with leptonic top decays involve only
positively charged leptons.
